To provide a gas engine heat pump and its control method, overcoming the disadvantage due to an excess in refrigerant circulation amount to a cooling load without any increase in rotational frequency of a gas engine.

When an allowable minimum refrigerant circulation amount of an operating compressor 1 is excessive to a required refrigerant circulation amount, and the rotational frequency of the gas engine is a predetermined value or more in the case of decreasing the number of operating compressors 1 (in the region between B and F), the excessive refrigerant is caused to flow through a heat exchanger 6 without decreasing the number of the operating compressors 1, and cooling water of the gas engine 2 is caused to flow through the heat exchanger 6.