A first slave piston (88b) and a second slave piston (88a) are disposed in tandem in series within a cylinder body (82), and the pistons are arranged so that part of the shaft section (105) of the second slave piston (88a) overlaps with the inner periphery of an opening section (95) provided in the backward side, in the displacement direction, of the first slave piston (88b). A long hole (107) extending along the axial direction of the second slave piston (88a) is provided in the shaft section (105), and a connection pin (79) which regulates the initial position of the second slave piston (88a) is inserted into the long hole (107).
