According to one embodiment, a power supply circuit is adapted to turn on a switching transistor connected between an input terminal and an output node and supply current via an inductor to a capacitor connected to the output node, so as to obtain an output voltage from an output terminal connected to the capacitor. A detection signal according to current flowing in the inductor or a detection signal according to a comparison result between the output voltage and a reference voltage are detected at a predetermined time, and an ON-time of the transistor is controlled in accordance with the detection signal.