The collector, emitter, and base of a bipolar transistor circuit are connected to a high side power supply terminal, the drain of a level shift transistor, and a floating power supply terminal, respectively. When a high side output transistor is on, the floating power supply terminal is at the potential of a high potential power supply terminal. The high side power supply terminal is at a potential higher than the potential of the floating power supply terminal by a constant voltage. Turning the level shift transistor on, its drain potential drops below the potential of the floating power supply terminal; The base current flows through the bipolar transistor circuit and the drain potential of the level shift transistor is clamped near the potential of the floating power supply terminal; The bipolar transistor circuit is turned on and its collector current supplies the drain current of the level shift transistor.