PURPOSE: To make it possible to vary the capacity of a compressor easily by a method wherein a switching mechanism is provided in a sucking hole of a cylinder and the quantity of gas intake by the cylinder is controlled by opening and closing the sucking hole.

CONSTITUTION: When load lowers, a control circuit generates a signal to thereby operate the switching mechanism 17. That is, a power cylinder 24 rotates a valve ring 18 by a predetermined angle through a wire 25. Accordingly, the positions of guide holes 22a are displaced with sucking holes 22, respectively, to thereby close the latter holes completely. As a result, the compression of a coolant gas within a first cylinder 10 is stopped keeping only the compression of same in a second cylinder 11 continued, with the result that the compressor is operated with reduced capacity.