A control IC includes a VS voltage detection circuit that indirectly detects input voltage, by utilizing a fact that a voltage of a VS terminal of a reference potential of a high side drive circuit changes to a voltage equivalent to the input voltage when a high side drive signal is output from a control circuit to cause the high side drive circuit to turn on a high side switching element. The VS voltage detection circuit determines the level of the input voltage by sampling the VS terminal voltage at a time point that is delayed by a predetermined time from a rising edge of the high side drive signal, and supplies the determined level to the control circuit.