To simplify a measuring system by controlling a thermal storage and heat radiating operation based on the relation between primary medium temperature and thermal storage level and the measured temperature of the primary, medium when a heat exchanging is carried out between a primary medium system for circulating the primary medium between a heat storage tank and a refrigerating machine, and a secondary medium system for circulating a medium to a secondary medium air conditioning space.

Primary medium of -5°C is supplied to ice thermal storage tanks 2 from a refrigerating machine 3 during heat storage operation. The primary medium is subjected to a heat exchange therein and discharged at a temperature of -2°C. Thus, ice between pipelines comes into contact with the primary medium, so that the cooling areas of the pipelines are decreased and the outlet temperature of the ice thermal storage tank is lowered. During a heat radiating operation, the ice between the pipelines becomes water so that the outlet temperature of the ice thermal storage tank rises. Thus, thresholds are respectively determined by a heat storage completion temperature setting device 34 during the heat storage operation, and by a heat radiating completion temperature setting device 35 during the heat radiating operation based on the outlet temperature of the ice thermal storage tank of the primary medium when heat storage level reaches a prescribed value. Then, a storage detecting part 33 outputs a heat storage completion signal and a heat radiation completing signal based on an input signal from a temperature converter 32 and the thresholds by the temperature setting devices 34 and 35.