FRICTIONAL ENGAGEMENT DEVICE

A friction engagement device (1) includes an elastic member (20) between a piston (10) and a friction plate (51) in an axial direction (L). The elastic member (20) includes: a second engaged portion to be brought into engagement with an engagement portion of a tubular member (30) so as to be movable in the axial direction (L); and an annular plate portion sandwiched between a pressing surface (14) of the piston (10) and the friction plate (51) from both sides in the axial direction (L). A surface of the annular plate portion facing a first axial side (L1) is provided with a projection and a recess arranged alternately in a circumferential direction. Assuming that a phase where a radial groove (14b) provided in the pressing surface (14) and a projection provided on the annular plate portion are located at corresponding positions in the circumferential direction is a particular phase, the engagement portion of the tubular member (30), a first engaged portion of the piston (10), and the second engaged portion of the elastic member (20) are formed such that the piston (10) and the elastic member (20) are unable to come into engagement with the tubular member (30) at the particular phase.