PURPOSE: To cause the turning-on resistance of a switch to be low by connecting one electrode of boost lap capacity to a common connecting node and giving a signal, whose phase is reverse to the input signal of a complementary inverter, from a reverse phase signal forming means to the other electrode of the boostrap capacity.

CONSTITUTION: When an MOSFETQ12 is controlled to a turning-on condition by the output of a CMOS inverter INV10, boostrap capacity Cb is charged to a power source voltage Vcc level. Next, when the output of the CMOS inverter INV10 is inverted, in correspondence to this inversion, a coupling node N1 of an MOSFETQ10 and the Q12 is boosteed to be ≥ the power source voltage Vcc by the operation of the boostrap capacity Cb and at such a time, the MOSFETQ12 is controlled to a turing-off condition. Thus, the charge of the boosting node N1 does not flow through the MOSFETQ12 to a power source voltage Vcc terminal and an output amplitude, which is boosted to be ≥ the power source voltage Vcc, is obtained in the output terminal of the CMOS inverter INV10. Thus, the turning-on resistance of the switch can be made enough low.