To provide a hot water supply apparatus and a water flow rate regulation/switch valve used in the same with small number of parts, not requiring a large part-disposing space, capable of downsizing, having large freedom of design, and enabling part cost and assembling man-hour to be reduced.

In a branch part wherein a hot water supply route S1 branches out into a general purpose hot water supply route S2 and a bath hot water supply route S3, a water flow rate regulation/switch valve 10 is disposed, wherein the valve 10 has a function for switching the general purpose hot water supply route S2 and the bath hot water supply route S3, a water flow rate regulating function for maintaining a specified hot water temperature by reducing a water rate when a hot water delivery temperature is lower than the specified hot water temperature even by burning fuel at full capacity, and a function of a back flow preventing valve for preventing water (hot water) from backflowing to a heat exchanger through the general purpose hot water supply route S2 and the hot water supply route S1 when supplying bath hot water.