To provide a multi-disk frictional engagement device simplified in structure, reduced in size, and expected to reduce the number of components and production cost.

A plurality of driven plates 11 to 16 spline-fitted to a spline groove 2 formed in the inner periphery of a transmission case 1 and drive plates 21 to 26 spline-fitted to a spline groove 7 formed in the outer periphery of a rotating body 5 are arranged alternately each other. A piston 41 is arranged on one side thereof and a retaining plate 17 spline-fitted to the spline groove 2 is arranged on the other side. Also, a snap ring 30 having the function of a dish plate in which the outer peripheral edge 32 thereof is locked to the ring groove and the inner peripheral edge 31 abuts on the side face 17a of the retaining plate 17 is installed.