A power supply apparatus has a battery and a temperature detection circuit. The battery has n battery cells, and the temperature detection circuit has m temperature detection units. Each temperature detection units has a temperature sensor that is thermally coupled to one or more of the battery cells and whose electrical resistance decreases as the temperature of the battery cell or battery cells to which it is thermally coupled increases, a serial resistor that is connected in series with the temperature sensor, and a first diode whose cathode is connected to the node between the temperature sensor and the serial resistor. The serial circuit formed by the temperature sensor and the serial resistor receives a predetermined voltage such that, as the electrical resistance of the temperature sensor decreases, the voltage at the node decreases. The first diodes have anodes thereof connected together.