PURPOSE: To avoid the lowering in an output signal and undershooting, by providing a transistor (TR) controlling a boosting signal to the opposite direction of the output of a bootstrap capacitance.

CONSTITUTION: A node N2 is charged by the rise of a boosting signal B to boost an output signal 0. The 0 goes to low level through the discharge by the rise of a set signal '. A capacitor C1 can be controlled with TRs Q2 and Q5, independently of the state of the signal B. Thus, even is the signal B falls faster than the rise of the reset signal ', the level of the output signal 0 is not lowered. EVen if the boosting signal B falls faster than the fall of the reset signal ', since a TR Q4 is interrupted by a control signal 1 of a low level, no undershoot can be caused.