To prevent hunting of a slide valve.

A slide valve control and operation unit 12 of an arithmetic unit 11 obtains the movement command quantity of the slide valve 21. A hunting preventive unit 13 monitors the hunting of the slide valve based on the movement command quantity. When the hunting occurs, the movement command quantity is corrected to a smaller command quantity, and output to a capacity control unit 14. The movement quantity of the slide valve at the hunting is thus smaller than the movement quantity in a normal operation by the capacity control unit 14. Therefore, the hunting of the slide valve 21 is prevented.