To provide a lock-up device which can be miniaturized while securing large allowable transmitting power.

The lock-up device 7 includes a piston 30, a spring 33, a first friction plate 51, and a second friction plate 52. The piston 30 is supported movably and rotatably in the axial direction by a turbine 4 and structured to move in the axial direction according to the change of pressure. The first friction plate 51 is arranged in the axial direction between the piston 30 and a front cover 2. The second friction plate 52 is arranged in the axial direction between the piston 30 and the front cover 2.