A compressor capacity control method and a device is provided. The changeover from a loading state regarding the compressor to an unloading state regarding the compressor and vice versa is controlled, whereby, during a time span from a starting time point when the compressor operation state changes into an unloading state to a time point when a loading/unloading operation-cycle is finished and a predetermined time duration has passed after the starting time point, the time cycle control is performed so that the loading state is changed into the unloading state, at a time point when the predetermined time duration has passed. Further, the discharge pressure of the fluid discharged from the compressor is detected so that the loading state is changed into the unloading state in a case where the discharge pressure exceeds a prescribed upper limit pressure.