PURPOSE: To make it possible to heat a compartment even when an engine is cold, by providing an auxiliary heating means in a passage bypassing a heat exchanger and allowing air down-stream of a blower to pass through the auxiliary heating means and hot air to blow out from an opening inside of an air conditioner case.

CONSTITUTION: An auxiliary heating passage 15 is opened to an air conditioner case 1 downstream of a blower 5 at one end 15a thereof, and is connected at the other end 15b with a lower blowing opening 11 downstream of a heat exchanger 8. The auxiliary heating means 17 is constituted in such that fuel is supplied to a burner 26 located in a combustion chamber 19 of a combustion device 18, and is ignited by an ignition device 22, and air fed through the passage 15 is heated by an auxiliary heat exchanger 25. When engine cold starting is detected by an engine coolant temperature and atmospheric temperature, etc., the combustion device 18 starts combusting under predetermined conditions and continues combustion until the engine coolant temperature increases sufficiently to enable heating by hot air.