A cam member 5 is disposed within a first chamber R1 such that the cam member 5 is rotatable but non-movable in the axial direction. The cam member 5 is non-rotatably connected to a rotor 3 through a connection shaft portion 52 piercing into a piston 4. A second cam mechanism 10 is disposed between the cam member 5 and the piston 4. When the cam mechanism 7 causes the piston 4 to move from the second chamber R2 side to the first chamber R1 side in accordance with rotation of the rotor 3 in one direction, the second cam mechanism 10 allows the piston 4 to move from the second chamber R2 side to the first chamber R1 side by the same amount of movement. When the second cam mechanism 10 causes the piston 4 to move from the first chamber R1 side to the second chamber R2 side in accordance with rotation of the rotor 3 in the other direction, the cam mechanism 7 allows the piston 4 to move from the first chamber R1 side to the second chamber R2 side by the same amount of movement.