The present invention is directed to provide a device for reducing pulsation in a variable displacement compressor. The compressor is connected to an external refrigerant circuit. The device for reducing pulsation includes a flow passage and a control valve. The control valve includes a valve housing, a spool valve and a damper chamber. The spool valve has formed therethrough a flow hole. The damper chamber communicates with the flow passage adjacent to the external refrigerant circuit through the flow hole. Effective cross-sectional area and effective length of the flow hole are determined based on frequency of a specific pulsation of the refrigerant gas and volume of the damper chamber at the time of the development of the specific pulsation in such a manner that the specific pulsation is developed, resonance effect of a Helmholtz resonator takes place in the damper chamber.