A hot water supply device 1 includes a fin-and-tube type heat exchanger (b 21) that applies heat to fresh water with combustion gases, and a heat exchanger casing (b 22) for housing the heat exchanger (b 21), and in order to be able reliably to determine by a simple method whether the hot water supply device is clogged by lime scale, there are provided a temperature detector (b 31) for detecting the surface temperature of the heat exchanger casing (b 22) and a control unit (b 7) that determines that scale has built up in the heat exchange tubing (b 27) of the heat exchanger (b 21) when the temperature detected by this temperature detector (b 31) is greater than a set temperature.