To restrain drag torque while sufficiently ensuring a torque transmitting capacity in a lock-up device of a torque converter.

This lock-up device 4 for a torque converter 1 comprises a first piston 43 and a piston 42. The first piston 43 can move within a space C by a pressure change of the space C of the torque converter 1, and is arranged in the vicinity of a friction surface of an input front cover 2. the piston 42 can move within the space C by the pressure change of the space C, and can push the first piston 43 toward the friction surface of the input front cover 2.