-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 SI+0NVf9137nEGvVwhzRKb/6FffBJBePNG5/ahlowlrr1G1OsW8wOVGUx5RSf0AZ
 57SEFeWRhCyrCZa8D9giKg==

<SEC-DOCUMENT>0000897077-10-000008.txt : 20100408
<SEC-HEADER>0000897077-10-000008.hdr.sgml : 20100408
<ACCEPTANCE-DATETIME>20100408175220
ACCESSION NUMBER:		0000897077-10-000008
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100407
FILED AS OF DATE:		20100408
DATE AS OF CHANGE:		20100408

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			DOUGLASS DONALD J
		CENTRAL INDEX KEY:			0001000392

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-13854
		FILM NUMBER:		10740505

	MAIL ADDRESS:	
		STREET 1:		330 ARGYLE AVE
		CITY:			SAN ANTONIO
		STATE:			TX
		ZIP:			78209

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ALAMO GROUP INC
		CENTRAL INDEX KEY:			0000897077
		STANDARD INDUSTRIAL CLASSIFICATION:	FARM MACHINERY & EQUIPMENT [3523]
		IRS NUMBER:				741621248
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1627 E WALNUT
		CITY:			SEGUIN
		STATE:			TX
		ZIP:			78155
		BUSINESS PHONE:		8303791480

	MAIL ADDRESS:	
		STREET 1:		P.O. BOX 549
		STREET 2:		1627 EAST WALNUT
		CITY:			SEGUIN
		STATE:			TX
		ZIP:			78155
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-04-07</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000897077</issuerCik>
        <issuerName>ALAMO GROUP INC</issuerName>
        <issuerTradingSymbol>ALG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001000392</rptOwnerCik>
            <rptOwnerName>DOUGLASS DONALD J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>330 ARGYLE AVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN ANTONIO</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>78209</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-04-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>31483</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.4784</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>145680</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Range in price for this transaction was $20.2775 - $20.59.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Donald J. Douglass</signatureName>
        <signatureDate>2010-04-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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