A selection circuit generates a voltage VS of a switching terminal VS or a power supply voltage VCC, whichever is higher, in a common line. A regulator stabilizes a voltage VCOML of a reference line at a level lower than a voltage VCOM of the common line by a predetermined voltage difference ΔV. A charge pump circuit is provided between the common line and the reference line and steps up a voltage difference ΔV between the common line and the reference line. A rectifying element charges a bootstrap capacitor between a bootstrap terminal and the switching terminal, with an output voltage of the charge pump circuit.