A no-load detection circuit includes an inductance device, an impedance device and a switch circuit. The inductance device is interposed between a choke coil and a first output terminal, which is at a high potential side, so as to be magnetically coupled to the choke coil. The impedance device is connected in series with the inductance device between the inductance device and the first output terminal. The switch circuit is configured to be turned on when a value of electric potential at the first output terminal exceeds a predetermined reference value. The control circuit is configured to stop the switching control if the switch circuit is turned on.