Torque converter

In sliding engagement of a clutch plate of a lock-up clutch with a front cover of a converter housing, with a difference in rotational speed therebetween, the sum of the urging force of a coil spring and the force of a lock-up discharge hydraulic pressure in a front side chamber is greater than the force of a lock-up engagement pressure in a rear side chamber. A selector valve member, accommodated in a valve chamber of a displacement selector mechanism, therefore, brings an oil chamber between the clutch plate (first piston) and a second piston into communication with the front side chamber. The hydraulic pressure of the rear side chamber received by a rear face of the piston is higher than hydraulic pressure of the oil chamber received by a front face of the piston and, therefore, the piston is displaced forwardly into frictional contact with the clutch plate and transmission of judder to an input shaft of a speed change mechanism is thereby reduced.