PURPOSE: To facilitate temperature control and the control for engine load by applying the voltage signal for designating a compression capacity, onto a solenoid valve for opening and closing a communication hole to a crank chamber and an intake chamber.

CONSTITUTION: In order to capacity-control a swash-plate type compressor which is used for a car, etc. and driven by an engine, each detected output of an inside-air temperature sensor 76, outside-air temperature sensor 77, intake pressure sensor 78, etc. is input into a microcomputer 79, and comparison-calculated with the signal of a temperature setting device 91. Said output is input as compression-capacity designating signal Va into a comparator 73, and the signal Va is corrected by the signals supplied from an accelerator switch 92, and an overheat switch 93, and said signal Va is compared with the signal Vb of a triangular- wave generator 74 in a certain frequency, and the pulse signals having a pulse width corresponding to the compression capacity designation signal are output to opening/closing-control a solenoid valve 44.