A friction engagement device comprising: a friction plate; a tubular member supporting the friction plate; and a piston to press the friction plate from a first axial side that is one side in an axial direction, wherein the tubular member has a tubular shape extending in the axial direction and is disposed on a first radial side that is an outer side or an inner side in a radial direction relative to the friction plate, the tubular member includes an engagement portion on a peripheral surface of the tubular member located on a second radial side opposite to the first radial side in the radial direction, the engagement portion includes at least either a protrusive ridge or protrusive ridges protruding to the second radial side and extending in the axial direction or a recessed groove or recessed grooves recessed to the first radial side and extending in the axial direction, the piston includes a first engaged portion to be brought into engagement with the engagement portion so as to be movable in the axial direction, and a pressing surface formed to face a second axial side opposite to the first axial side in the axial direction so as to press the friction plate, the pressing surface is provided with a radial groove recessed to the first axial side and extending in the radial direction, the friction engagement device further comprises an elastic member disposed between the piston and the friction plate in the axial direction so as to be elastically deformed by a pressing force of the piston, the elastic member includes a second engaged portion to be brought into engagement with the engagement portion so as to be movable in the axial direction, and an annular plate portion sandwiched between the pressing surface and the friction plate from both sides in the axial direction, a surface of the annular plate portion facing the first axial side is provided with a projection protruding to the first axial side and a recess recessed to the second axial side, such that the projection and the recess are arranged alternately in a circumferential direction, and assuming that a phase where the radial groove and the projection are located at corresponding positions in the circumferential direction is a particular phase, the engagement portion, the first engaged portion, and the second engaged portion are formed such that the piston and the elastic member are unable to come into engagement with the tubular member at the particular phase. a friction plate; a tubular member supporting the friction plate; and a piston to press the friction plate from a first axial side that is one side in an axial direction, wherein the tubular member has a tubular shape extending in the axial direction and is disposed on a first radial side that is an outer side or an inner side in a radial direction relative to the friction plate, the tubular member includes an engagement portion on a peripheral surface of the tubular member located on a second radial side opposite to the first radial side in the radial direction, the engagement portion includes at least either a protrusive ridge or protrusive ridges protruding to the second radial side and extending in the axial direction or a recessed groove or recessed grooves recessed to the first radial side and extending in the axial direction, the piston includes a first engaged portion to be brought into engagement with the engagement portion so as to be movable in the axial direction, and a pressing surface formed to face a second axial side opposite to the first axial side in the axial direction so as to press the friction plate, the pressing surface is provided with a radial groove recessed to the first axial side and extending in the radial direction, the friction engagement device further comprises an elastic member disposed between the piston and the friction plate in the axial direction so as to be elastically deformed by a pressing force of the piston, the elastic member includes a second engaged portion to be brought into engagement with the engagement portion so as to be movable in the axial direction, and an annular plate portion sandwiched between the pressing surface and the friction plate from both sides in the axial direction, a surface of the annular plate portion facing the first axial side is provided with a projection protruding to the first axial side and a recess recessed to the second axial side, such that the projection and the recess are arranged alternately in a circumferential direction, and assuming that a phase where the radial groove and the projection are located at corresponding positions in the circumferential direction is a particular phase, the engagement portion, the first engaged portion, and the second engaged portion are formed such that the piston and the elastic member are unable to come into engagement with the tubular member at the particular phase.