PURPOSE: To permit to utilize the solar heat effectively in accordance with the utilizing purpose such as pouring into a bathtub or general hot-water supplying (re-heated by an auxiliary heat source if necessary) by a method wherein the solar heat is collected and accumulated separately into a low temperature tank and a high temperature tank.

CONSTITUTION: Switching of the hot-water supplying mode of the high temperature tank and the low temperature tank is effected by operating first changeover valve CV1 through a changeover switch provided in a remote controller 30. In the high temperature tank hot-water supplying mode, hot-water flows in the sequence of high temperature tank 14→first change-over valve CV1→pump PM2→second changeover valve CV2→hot-water supplying faucet 23 as shown by the diagram (a) and it may be utilized for pouring it into the bathtub 31 especially. In the low temperature tank hot-water supplying mode, hot-water flows in the sequence of low temperature tank 13→first changeover valve CV1→pump PM2→second changeover valve CV2→auxiliary heat source machine 11→hot-water supplying faucet 23 as shown by the diagram (b) it may be utilized for the hot-water supply of a kitchen or a toilet. The opening and closing of the hot-water supplying faucet 23 are detected by a pressure switch PS and the hot- water supplying pump PM2 is stopped or operated in accordance therewith.