PURPOSE: To permit the cut-in of general hot-water supply during high-temperature hot- water supplying safely and simply by only the operation of an opening and closing valve by a method wherein the opening operation of a general use hot-water supply opening and closing valve is detected and a switching valve is switched automatically into a condition capable of effecting general use hot-water supply based on the detection in a condition preferential to hot-water supply switching operating equipment.

CONSTITUTION: When the opening and closing valve 10 is opened during hot-water pouring or re-heating, second water flow switch 14 is put ON, in spite of a condition that the operating equipment 28 of hot-water supply switching 28 is located at a hot-water pouring position P2 and a re-heating position P3, to open a water amount regulating valve 6 widely while a switching valve 9 is switched and the general hot-water supply, supplying the hot-water, controlled to a preset temperature, from a hot-water supplying device 7, is effected. Furthermore, the switching valve 9 is switched only when the hot- water temperature is reduced to the set temperature, therefore, the high-temperature hot-water for pouring and reheating will never be supplied from the opening and closing valve 10.