PURPOSE: To attain high accuracy and high stability, by eliminating the difference in delay time by using a differential circuit for a driving circuit, taking balance between the rising and falling times and avoiding the change in pulse width even if the delay time is large.

CONSTITUTION: The driving circuit 11 is a bipolar circuit and a CR circuit comprising a resistor 12 and a varactor diode 13 is formed to each output. A bipolar signal from each CR circuit is inputted to a differential input type receiving circuit 11' of the next stage to perform waveform shaping. A voltage applied to the varactor diode 13 is given via a DA converter 14. The delay time is changed by changing an input D of the DA converter. When a reverse bias voltage is small and the capacitance is large, even if the waveform at points A and B is different between the rising and falling times since the receiving circuit 11' is formed as a differential input, no difference in the increment of delay time is produced between the rising and the falling times at outputs O1 and O2.