PURPOSE: To improve the rise response characteristics of an output voltage waveform without increasing the power consumption, by connecting a bias supplying field effect transistor to the input electrode of a switching element.

CONSTITUTION: When the input signal voltage Vi is switched to an H level at a time point t1, a transistor TRQ2 is turned on. At the same time, an MOSTRQ3 and a TRQ1 are turned off to set the output voltage V0 at 0V. Then the voltage Vi is changed to 0V at a time point t2, a TRQ2 is turned off. Then the gate voltage of a TRQ3 rises up suddenly to turn on the TRQ3. As a result, a sufficiently large base current is supplied to the base of a TRQ1. Thus the TRQ1 is suddenly turned on. Therefore the voltage V0 rises suddenly up to Va1 at the point t2. In such a way, it is possible to have a sudden rise of the voltage V0 without reducing the value of a bias supplying resistance RB. This circut prevents dullness at the front edge part of an output voltage waveform without increasing an increment of power consumption within a circuit.