An automatic transmission comprising a frictional engagement element , the frictional engagement element including: a first piston and a second piston each having a first face (14 1 , 15 1 ) and a second face (14 2 , 15 2 ) opposite to each other in an axial direction, the first and second pistons being movable in the axial direction; a plurality of friction plates disposed near the second faces (14 2 , 15 2 ) of the first and second pistons ; an engaging hydraulic chamber defined by the first faces (14 1 , 15 1 ) of the first and second pistons , the engaging hydraulic chamber being configured to be subject to a hydraulic pressure to move the first and second pistons in a direction of pressing the friction plates ; an opposite hydraulic chamber defined by the second faces (14 2 , 15 2 ) of the first and second pistons , the opposite hydraulic chamber being configured to be subject to a hydraulic pressure to move the first and second pistons in a direction of releasing the friction plates ; a first urging member for urging the first piston in the direction of releasing the friction plates ; and a second urging member for urging the second piston in the direction of releasing the friction plates with an urging force larger than the urging force of the first urging member , wherein one of the first and second pistons has a communicating hole (14c; 115c) for connecting the engaging hydraulic chamber with the opposite hydraulic chamber and the other of the first and second pistons has a valve part (15c; 114c) for closing the communicating hole (14c; 115c), the first and second urging members have different urging forces so that, in the process of disengagement of the frictional engagement element , a difference in travel distance between the first and second pistons in motion due to the different urging forces of the first and second urging members causes the valve part (15c; 114c) to open the communicating hole (14c; 115c) to thereby make hydraulic oil flow from the engaging hydraulic chamber into the opposite hydraulic chamber through the communicating hole (14c; 115c), and the first and second urging members have different urging forces so that, in the process of engagement of the frictional engagement element , a diference in travel distance between the first and second pistons in motion due to the different urging forces of the first and second urging members causes the valve part (15c; 114c) to open the communicating hole (14c; 115c) to thereby make hydraulic oil flow from the opposite hydraulic chamber into the engaging hydraulic chamber through the communicating hole (14c; 115c). a first piston and a second piston each having a first face (14 1 , 15 1 ) and a second face (14 2 , 15 2 ) opposite to each other in an axial direction, the first and second pistons being movable in the axial direction; a plurality of friction plates disposed near the second faces (14 2 , 15 2 ) of the first and second pistons ; an engaging hydraulic chamber defined by the first faces (14 1 , 15 1 ) of the first and second pistons , the engaging hydraulic chamber being configured to be subject to a hydraulic pressure to move the first and second pistons in a direction of pressing the friction plates ; an opposite hydraulic chamber defined by the second faces (14 2 , 15 2 ) of the first and second pistons , the opposite hydraulic chamber being configured to be subject to a hydraulic pressure to move the first and second pistons in a direction of releasing the friction plates ; a first urging member for urging the first piston in the direction of releasing the friction plates ; and a second urging member for urging the second piston in the direction of releasing the friction plates with an urging force larger than the urging force of the first urging member , <EOS>