Patent ID: 7549523

Claim:
A friction apply device of a vehicular automatic transmission, comprising: a bottomed cylindrical clutch piston which includes: a first member, which is a cylindrical member in which both ends are open, having a plurality of positioning protrusions that extend in an axial direction formed on an inner peripheral surface thereof, and an inner peripheral groove formed in an inner peripheral surface of one end portion; a second member which is a disc-shaped member that fits into the one end portion of the first member and abuts against end surfaces of the plurality of positioning protrusions such that the second member is prevented from moving in one axial direction; and a snap ring which fits in the inner peripheral groove and prevents the second member from moving in the other axial direction, wherein a projecting portion that projects toward an inner peripheral side, as well as a pressure applying protrusion which protrudes from the projecting portion toward the one end portion of the first member and applies pressure to a friction apply element are formed on the other end portion of the first member; and a clutch drum which holds an annular friction plate such that the annular friction plate is able to move in the axial direction but unable to rotate relative to the clutch piston and has a plurality of grooves formed parallel to an axial center in an outer peripheral surface thereof, the axial center being the same as the axial center of the clutch piston, wherein the plurality of positioning protrusions fit in the grooves.