PURPOSE: To easily generate signals whose frequency is an arbitrary even number multiple of a base frequency fC from the signals of the base frequency fC in an improve stage with simple circuit constitution.

CONSTITUTION: The input signals (d) of the frequency fC are converted into digial signals (e) whose duty is 50 by a comparator 11 and when the rise/fall change points are detected by a delay line 12 and an exclusive OR gate 13, only the higher order harmonic of an even number in terms of a frequency spectrum is included in a change point detection pulse train. Thus, the need of setting a pass-band width to a narrow band is eliminated and the desired higher harmonic can be easily extracted from the group of the higher harmonic of the even number order by a band-pass filter 14.