Embodiments of the invention provide a first piston with a smaller diameter and a second piston with a larger diameter that switch a spool between a first switching position at one end and a second switching position at the other end, and a return spring that moves the spool to a neutral switching position are provided, at the neutral switching position, some of a plurality of ports communicate with one another and remaining ports are closed; at the first switching position, the communication-and-closure relationship of the plurality of ports is the reverse of that in the neutral switching position; and at the second switching position, all the plurality of ports are closed, and when the spool is switched to the neutral switching position and the first switching position, only the first piston is operated, and when the spool is switched to the second switching position, the second piston is operated.