Komatsu Ltd. Shareholders' Equity [Tables]

12 Months Ended

Mar. 31, 2011

Komatsu Ltd. Shareholders' Equity (Tables) [Abstract]

Stock option activity

	2011							2010					2009
	Number of			Weighted average				Number of			Weighted average		Number of			Weighted average
	shares			exercise price				shares			exercise price		shares			exercise price
				Yen		U.S. dollars					Yen					Yen
Outstanding at beginning of year		3,333,000		¥	2,051	$	24.71		2,891,000		¥	2,022		2,844,000		¥	1,784
Granted		76,800			1		0.01		642,000			1,729		463,000			2,499
Exercised		(174,000	)		1,238		14.92		(200,000	)		595		(416,000	)		926
Outstanding at end of year		3,235,800			2,047		24.66		3,333,000			2,051		2,891,000			2,022
Exercisable at end of year		3,159,000			2,096		25.25		2,691,000			2,128		2,428,000			1,931

Options outstanding and options exercisable

	Outstanding												Options Exercisable
											Weighted average												Weighted average
			Weighted average				Intrinsic value				remaining				Weighted average				Intrinsic value				remaining
	Number of		exercise price				Millions of		Thousands of		contractual life		Number of		exercise price				Millions of		Thousands of		contractual life
Exercise Prices	shares		Yen		U.S. dollars		yen		U.S. dollars		years		shares		Yen		U.S. dollars		yen		U.S. dollars		years
¥1 - 650		76,800	¥	1	$	0.01	¥	216	$	2,602		7.3		—		—		—		—		—		—
¥651 - 900		300,000		673		8.11		646		7,783		1.3		300,000	¥	673	$	8.11	¥	646	$	7,783		1.3
¥901 - 1,350		575,000		1,126		13.57		977		11,771		2.3		575,000		1,126		13.57		977		11,771		2.3
¥1,351 - 2,325		1,259,000		2,032		24.48		998		12,025		4.8		1,259,000		2,032		24.48		998		12,025		4.8
¥2,326 - 3,700		1,025,000		3,136		37.78		151		1,819		4.9		1,025,000		3,136		37.78		151		1,819		4.9
¥1 - 3,700		3,235,800		2,047		24.66		2,988		36,000		4.1		3,159,000		2,096		25.25		2,772		33,398		4.1

Risk-free rate of the share option

	2011			2010			2009
Grant-date fair value	¥	1,785 ($21.51	)	¥	643		¥	813
Expected term	5 years			7 years			7 years
Risk-free rate		0.13%–1.11	%		0.17%–1.35	%		0.60%–1.48	%
Expected volatility		54.00	%		44.00	%		39.00	%
Expected dividend yield		0.96	%		2.07	%		1.32	%

Interest rate corresponding to discount periods is applied to risk-free rate

	1 year			2 years			3 years			4 years			5 years			6 years			7 years			8 years			9 years			10 years
2009		0.60	%		0.71	%		0.82	%		0.94	%		1.02	%		1.07	%		1.07	%		1.16	%		1.33	%		1.48	%
2010		0.17	%		0.24	%		0.32	%		0.48	%		0.63	%		0.74	%		0.88	%		1.03	%		1.19	%		1.35	%
2011		0.13	%		0.14	%		0.18	%		0.25	%		0.36	%		0.47	%		0.59	%		0.76	%		0.94	%		1.11	%