The driver D1 for driving the sWitch S1 includes a boost capacitor CB. The boost capacitor CB is charged When the sWitch S1 is OFF (When the MOS transistor is turned off) and the sWitch S2 is ON (When the MOS transistor is turned on), as explained by referring to FIG. 3. On the contrary, the boost capacitor CB is discharged When the driver D1 holds the sWitch S1 ON. Namely, the driver D1 generates an electric potential higher than an input voltage Vin by using the electric charge stored in the boost capacitor CB.