Refrigeration cycle apparatus

A refrigeration cycle is switched from a refrigeration cycle circuit to a hot gas heater circuit to make the hot gas discharged from a compressor flow into an evaporator and heat the vehicle passenger compartment, at which time, when a suction pressure (Ps) of the compressor becomes a low pressure below a first predetermined pressure, the discharge volume (Vc) of the compressor is made larger to ensure a sufficient auxiliary heating performance. Further, when the hot gas is made to flow into the evaporator to heat the vehicle passenger compartment, if the suction pressure (Ps) of the compressor becomes a higher pressure over a second predetermined pressure, the discharge volume (Vc) of the compressor is made smaller to protect the refrigeration cycle parts and lighten the ON, OFF shock.