PURPOSE: To supply hot water in a reasonable manner, by disposing a heating source in a heat accumulating tank at a position thereof located above a solar heat exchanger, and disposing a hot-water supply port at the height equal to or slightly higher than that of the heating source.

CONSTITUTION: A heat exchanger 3 disposed at a lower portion in a heat accumulating tank 1 is connected to a solar heat exchanger 12, and a heating source 4 like an electric heater is disposed above the heat exchanger 3. The heat accumulating tank 1 has a water inlet port 2 at its lower portion and a hot- water outlet port 5 at its top, and a hot-water supply port 6 is formed in the side wall of the tank 1 at the height equal to or slightly higher than that of the heating source 4. The hot-water supply port 6 and the hot-water outlet port 5 are connected to places where hot water is used, via pipes 13 and a three-way valve 14. In the above arrangement, the solar heat collector 12 may be connected directly to the heat accumulating tank 1.