PURPOSE: To perform an active utilization of accumulated effective cold heat by a method wherein there are provided means for sensing a super-cooling degree index of refrigerant passed through a condenser during a released cooling operation, means for judging a residual amount of effective cold heat left in a cold heat accumulation tank and means for stopping a released cooling operation in response to a result of judgment.

CONSTITUTION: In a heat pump circuit of a released cooling operation mode, a third solenoid valve V3 and a fourth solenoid valve V4 are opened, a first solenoid valve V1, a second solenoid valve V2, a fifth solenoid valve V5 and a sixth solenoid valve V6 are closed and then a heat exchanger 4 is operated as a condenser CD. Then, a refrigerant pump PMP is driven, the refrigerant is circulated through a check valve V7, the condenser 4(CD), a second expansion valve EX2, an indoor evaporator EV1, and a second accumulator ACC 2 in this order and then a cooling operation is carried out only with cold heat accumulated in the cold heat accumulation tank 3. Then, if an effective cold heat residual amount judgment part 8 judges that the residual amount of effective cold heat left in the cold heat accumulation tank 3 is completely consumed, the operation stopping part 9 outputs an operation stop signal SIP to the refrigerant pump PMP so as to stop the operation of the refrigerant pump PMP.