A first piston connected to a first shaft and a second piston connected to a second shaft are supported within a housing by using a first leaf-spring unit and a second leaf-spring unit, respectively. Therefore, axial movement of the first shaft or the second shaft can be allowed, while circumferential rotational movement and radial movement can be restricted. The first leaf-spring unit includes two leaf-spring groups that are disposed in a row around the first shaft in the direction of the axis of the first shaft; similarly, the second leaf-spring unit includes two leaf-spring groups that are disposed in a row around the second shaft in the direction of the axis of the second shaft. Therefore, inclinations of the first shaft and the second shaft can be decreased. This results in reduction in contact between the first and second shafts and a cylinder within the housing and friction due to the contact.