<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2013-07-31</periodOfReport>

    <dateOfOriginalSubmission>2013-10-24</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001490286</issuerCik>
        <issuerName>TORTOISE MLP FUND, INC.</issuerName>
        <issuerTradingSymbol>NTG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001097362</rptOwnerCik>
            <rptOwnerName>SUN LIFE FINANCIAL INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>SUN LIFE ASSURANCE CO OF CANADA</rptOwnerStreet1>
            <rptOwnerStreet2>150 KING STREET WEST SUITE 1400</rptOwnerStreet2>
            <rptOwnerCity>TORONTO</rptOwnerCity>
            <rptOwnerState>A6</rptOwnerState>
            <rptOwnerZipCode>M5H 1J9</rptOwnerZipCode>
            <rptOwnerStateDescription>ONTARIO, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001381352</rptOwnerCik>
            <rptOwnerName>Sun Life Assurance CO of Canada</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>150 KING STREET WEST</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>TORONTO</rptOwnerCity>
            <rptOwnerState>A6</rptOwnerState>
            <rptOwnerZipCode>M5H 1J9</rptOwnerZipCode>
            <rptOwnerStateDescription>ONTARIO, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>4.29% Senior Notes Series D due Dec. 15, 2020</value>
            </securityTitle>
            <transactionDate>
                <value>2013-07-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000000</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1079960</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <valueOwnedFollowingTransaction>
                    <value>14000000</value>
                    <footnoteId id="F1"/>
                </valueOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote.</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>2.48% Senior Notes Series A due Dec. 15, 2013</value>
            </securityTitle>
            <transactionDate>
                <value>2013-08-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10000000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <valueOwnedFollowingTransaction>
                    <value>0</value>
                </valueOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Incorrectly reported as $13,000,000 on amendment dated 11/21/2013.</footnote>
        <footnote id="F2">Incorrectly reported in shares rather than US dollars on amendment dated 11/21/2013</footnote>
        <footnote id="F3">$13,000,000 directly owned by Sun Life Assurance Company of Canada, a wholly-owned subsidiary of Sun Life Financial Inc. and $1,000,000 directly owned by Sun Life and Health Insurance Company (U.S.), an indirectly wholly-owned subsidiary of Sun Life Financial Inc.</footnote>
        <footnote id="F4">Securities were owned by Sun Life Assurance Company of Canada, a wholly-owned subsidiary of Sun Life Financial Inc., prior to prepayment.</footnote>
        <footnote id="F5">Paid by the direct owner, Sun Life and Health Insurance Company (U.S.) and not by the indirect owner, Sun Life Financial Inc.</footnote>
    </footnotes>

    <remarks>$10,000,000 of 2.48% Senior Notes Series A due Dec. 15, 2013 were incorrectly reported as due Dec. 15, 2020 and as owned indirectly by Sun Life Financial Inc., and directly by Sun Life Assurance Company of Canada, on August 2, 2013 in Form 4 filing made on October 24, 2013, when such Series A Notes had previously been prepaid in full by the issuer and were no longer outstanding.

As noted in November 21, 2013 amendment, Sun Life and Health Insurance Company (U.S.) does not have a CIK or CCC number.  Its address is One Sun Life Executive Park, Wellesley Hills, MA 02481.</remarks>

    <ownerSignature>
        <signatureName>/s/Stephen C. Peacher, Authorized Signer for Sun Life Financial Inc., Sun Life Assurance Company of Canada and Sun Life and Health Insurance Company (U.S.)</signatureName>
        <signatureDate>2013-11-27</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/John T. Donnelly, Authorized Signer for Sun Life Financial Inc., Sun Life Assurance Company of Canada and Sun Life and Health Insurance Company (U.S.)</signatureName>
        <signatureDate>2013-11-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
