To effectively reduce vibration generated on a swash plate by regulating a roughness degree on a sliding surface so as to change sliding friction of a sliding surface between a trunnion shaft of the swash plate and bearing member.

A supporting structure of a swash plate in a swash plate type piston pump motor is formed in such a constitution that a bearing member 3 fitted to a bearing hole 2 formed on a case 1 is provided, and a turning shaft 6 formed on a swash plate 5 is fitted into the inner diameter part 4 of the bearing member 3, and is rotatably supported. In this case, the bearing member 3 is formed of hard resin, a member coated by resin, copper alloy, or the like, and surface treatment is carried out by soft blast means for spraying metal particle having a predetermined size such as, for example, aluminum and the like, for a predetermined time so as to set the surface roughness degree of the inner diameter part 4 of the bearing member 3 to 1.6a to 2.5a. A roughness degree changing means may be brushing by a hard blush, grinding by a grinding stone, and the like. Therefore, sliding friction of the sliding surface is changed so as to suppress generation of vibration.