PURPOSE: To reduce the size and the weight of a valve and to form a device in a compact state by a method wherein a stroke is reduced by an amount equivalent to one piston compared with a conventional type through reduction of the number of pistons to one.

CONSTITUTION: When a pressure is fed to a first pressure chamber A through a pilot valve connection pipe 9 mounted on a second casing 14, a piston 5 and a slide valve 6 are brought into a state shown by a solid line owing to a pressure in a first pressure chamber A being increased and a pressure in a second pressure chamber B being decreased, and a refrigerant flows through an outlet pipe 2 by means of an inlet pipe 1. When, in this state, pressure is fed to a second pressure chamber B through a pilot valve connection pipe 9', pressure in the second pressure chamber B is increased, pressure in the first pressure chamber A is decreased, and the piston 5 is moved as shown by a broken line. Along with the movement, the slide valve 6 coupled to the piston 5 through a shaft 7 is also moved from an outlet pipe 3 to the outlet pipe 2. A flow passage is varied such that a refrigerant is caused to flow from the inlet pipe 1 through the outlet pipe 3.