Abstract: The present invention includes a heat storage tank (1) with a built-in suction chamber (2), a first heat source unit (R-1) and a first pump (P-1) for pumping up water from the high-temperature side (3) of said heat storage tank (1) and supplying the chilled water into said suction chamber (2), a low-temperature heat exchanger (5) for exchanging heat between water and an antifreeze solution, a second pump (P-2) for pumping up water from said suction chamber (2) and supplying the water chilled by the antifreeze solution in said low-temperature heat exchanger (5) to the low-temperature side (4) of said heat storage tank (1) and a second heat source unit (R-2) and a third pump (P-3) for cooling the antifreeze solution in an antifreeze solution tank (6) and feeding it to said low-temperature heat exchanger (5), and is designed to variably control the flow rates of said first and second pumps (P-1 and P-2) in dependence upon their suction temperatures.