PURPOSE: To automatically select a suitable heat source of a plurality of heat sources to meet a state by providing a controller for automatically changing- over an operation of a heat exchanger of an air heat source and an operation of a heater of refrigerant in response to the state.

CONSTITUTION: A plurality of heat sources, i.e., outdoor heat exchangers 14, 16 and a boiler unit 18 are automatically and selectively heated in response to a state according to a control command of a controller 20. For issuing control command for changing-over the heat sources the controller 20 has, for example, a microcomputer for outputting a control command to change-over the heat sources. The microcomputer judges which of the heat sources is to be used to conduct an efficient heating operation according to a load state of a room heat exchanger 64 (and/of a room heat exchanger 68), outside air temperature, frequencies of compressor 26, 30, etc. Thus, a user can economically conduct a comfortable heating without necessity of a complicated change-over operation.