PURPOSE: To permit control in accordance with load fluctuation by a method wherein the opening degree of an electronic expansion valve is controlled based on the outputs of a first temperature sensor provided in a refrigerant heater and a second temperature sensor provided at the suction side of a compressor while the upstream side of the first temperature sensor is connected between an outdoor heat exchanger and the electronic expansion valve.

CONSTITUTION: A first temperature sensor 20 for detecting a refrigerant vaporizing temperature is provided in a refrigerant heater 6 and a second temperature sensor 23 is provided in the suction side of a compressor 1 while respective sensor signals are inputted into a controller 22. The opening degree of an electronic expansion valve 4 is controlled by the controller 22 so that a difference between the refrigerant vaporizing temperature and the suction temperature of the compressor becomes a set temperature difference. In this case the upstream side position of the first temperature sensor 20 is connected to a position of an outdoor heat exchanger 3 side than a connecting part 8 between the outdoor heat exchanger 3 and the electronic expansion valve 4 through a bypass passage 26 while a non-return valve 27 and a choke 28 are interposed in the bypass passage 26. According to this method, the opening degree of the electronic expansion valve 4 can be regulated in accordance with the change of capacity as well as the fluctuation of a load whereby the stabilized operation of a refrigerating cycle can be secured.