An object of this power supply device is to enable an overheat protection level and an overvoltage protection level to be set accurately. This power supply device includes a Schottky barrier diode (D52), which is placed as a temperature detection element at a region where a temperature is measured, to which a reverse voltage is applied, and through which a reverse leakage current flows; a comparator (Z51) which sets a potential of an output terminal thereof to a low level when a voltage corresponding to the reverse leakage current becomes equal to or more than a reference voltage; and a light-emitting diode (PC2) which is connected between an output terminal (8a) and the output terminal of the comparator (Z51), and has a current of a predetermined value or more flowing therethrough to emit light because the output potential of the comparator (Z51) is set to the low level, wherein an operation of a control circuit (12) is stopped by a thyristor (TH1) which is turned on, based on the current flowing through a phototransistor PC1, in response to the light emission of the light-emitting diode (PC2).