PURPOSE: To enable collection of a refrigerant necessary for a heating operation and execution of a stable heating operation by a method wherein a refrigerant collecting operation at the time of start of the heating operation is executed for a prescribed time or longer and until the temperature of a compressor reaches a prescribed temperature or above.

CONSTITUTION: When the operation of a refrigerant collecting means 33 is started by operating a compressor 1, a first timer element 37 starts counting of a prescribed time, and after the counting is ended, a second timer element 38 starts counting of another prescribed time. In the course of the counting of the prescribed time, a detected temperature of the compressor 1 detected by a temperature detecting means 34 is compared with a prescribed temperature in a comparator element 39. At the time point when the detected temperature exceeds the prescribed temperature, the refrigerant collecting means 33 is stopped by a switch element 36. When the detected temperature is below the prescribed temperature, counting of the second prescribed time is executed again, and after the end of the counting, the refrigerant collecting means 33 is stopped by the switch element 36. By this method, sufficient collection of a refrigerant can be executed for the heating circuit side at the time of start of a heating operation, and also the heating operation can be executed stably.