PURPOSE: To increase a heat storing capacity of a heat storage tank without enlarging the heat storage tank and without causing a heat loss and failure of an air-conditioning apparatus and consequently miniaturize the heat storage tank.

CONSTITUTION: A refrigerant 12 in a heat storage tank 10 is circulated between the heat storage tank 10 and a cooling apparatus 32. A bypass pipe 48 is connected to the downstream side of the cooling apparatus 32 and also to a mixing device 50. The refrigerant 12 immediately after being sucked from the heat storage tank 10 and the refrigerant 12 of which the temperature is raised by the cooling apparatus 32 are mixed by the mixing device 50. Temperature information from a thermometer 52 is outputted to a controller 54, which controls an on-off amount of each valve of the mixing device 50 on the basis of the temperature information, and thereby a feedback control is executed so that the temperature of the refrigerant 12 to be supplied to the cooling apparatus after mixing be a working temperature. According to this constitution, the temperature of the refrigerant 12 supplied to the cooling apparatus 32 is regulated to be about the working one practically and supplied, although the refrigerant 12 immediately after being sucked from the heat storage tank 10 is of extremely low temperature.