of the rear planetary carrier k 3 b 4 represents a fourth brake which locks the clockwise and counterclockwise revolution of the rear planetary carrier k 3 f 1 represents a first one way clutch which locks the counterclockwise revolution of the front and rear planetary sun gear s 12 f 2 represents a second one way clutch which locks the counterclockwise revolution of the front and rear planetary sun gear s 12 f 3 represents a third one way clutch which locks the counterclockwise revolution of the o d planetary carrier in relation to o d sun gear s 3 cg 1 and cg 2 respectively represents a counter drive gear and a counter driven gear for transmitting the engine torque which were changed its rotation speed to a drive pinion which is an output shaft of the automatic transmission as shown in fig2 for example to attain the first gear speed in the l range the first clutch c 1 the third clutch c 3 the third brake b 3 the second one way clutch f 2 and the third one way clutch f 3 should be engaged fig3 a to fig5 b concern the first embodiment which embodies the third brake b 3 of the automatic transmission at shown in fig1 in fig3 a reference numeral 1 represents a piston the piston 1 selectively pushes a first cam member 2 a second cam member 4 and a cam roller 3 located between the first cam member 2 and the second cam member 4 a spring 5 always pushes the first cam member 2 and the second cam member 4 including the cam roller 3 to the left of the figure reference numerals 6 and 7 respectively represent.