A detection circuit includes a current source with no temperature coefficient; a current generation circuit that generates a VBE proportional reference current from the current source with no temperature coefficient; a current mirror circuit that returns an output current of the current generation circuit; a reference voltage generation circuit that generates a VBE proportional voltage with a negative temperature coefficient on the basis of the current returned by the current mirror circuit so that the VBE proportional voltage is used as a reference voltage of a comparator; and a full-wave rectifying means, having a differential pair and a rectifier circuit, using the current source with no temperature coefficient, having an alternating current signal supplied as an input signal, for generating a direct current voltage with a negative coefficient on the basis of a voltage obtained by full-wave rectifying the alternating current signal, and for using the generated voltage as a comparative voltage of the comparator.