A hydraulic system includes a piston, a swash plate opposed to the piston, and a swash plate supporting member supporting the swash plate so that a tilt of the swash plate is variable. An oil reservoir portion is provided between the swash plate and the swash plate supporting member, the oil reservoir portion communicating with a pressure oil introducing passage. An area of the oil reservoir portion between the swash plate and the swash plate supporting member varies with the tilt of the swash plate.