PURPOSE: To increase the result coefficient by increasing the over-cooling quantity of a coolant without increasing the dimension of a heat exchanger.

CONSTITUTION: An inside room heat exchanger 21 used as an inside room condenser for heating and an inside room heat exchanger 22 used as an inside room evaporator for cooling are connected in series by the first and the second expansion valves 23 and 25 having bypass valves 24 and 26, respectively, so that both the heat exchangers 21 and 22 can be used as the inside room condenser for heating. A compressor 1, four-way valve 2 for selecting cooling and heating, outside room heat exchanger 5, and an air flow passage 14 for air conditioning are provided.