To operate a heat accumulating system for air conditioning where optimum operation can be performed, according to load fluctuation, and air conditioning capacity and operation efficiency are raised, by producing a specified flow rate of a heating medium passing through a heat source apparatus, at the time of operation requiring the operation of the heat source apparatus.

At the time of high-load operation requiring the operation of a heat source apparatus 11, the opening of a valve 17 for takeout of heat is adjusted, according to the heat load of a heat exchanger 16, and also the rotational speed of a pump 15 for takeout of heat is changed so that the flow of the heating medium passing through the heat source apparatus 16 may be in a set range. At the time of low-load operation not requiring the operation of the heat source apparatus 11, the operation of the heat source apparatus 11 is stopped to zero the quantity of the heating medium flowing to the heat source apparatus 11, and also the rotational speed of the pump 15 for takeout of heat is changed, according to the heat load of the heat exchanger 16, so as to adjust the quantity of the circulating heating medium.