To prevent deformation of a plate by thermal stress, in one-side stuck type friction engaging device.

In one-side stick type friction engaging device, an internal tooth disk 52 securing a friction material 56 in an axial direction one side and an external tooth disk 54 securing a friction material 56 in an axial direction one side are alternately arranged, the internal/external tooth disks 52, 54 are engaged by a piston, so as to transmit torque, in an external peripheral side of a plate of the internal tooth disk and in an internal peripheral side of a plate of the external tooth disk, respectively a notch is provided. In a side generating a high temperature due to partial contact, thermal distortion is relaxed by the notch formed in the plate, as a result, deformation of the plate is prevented.