PURPOSE: To simplify and alternation of the repetitive frequency with an optional function waveform, by controlling the ON/OFF of the input/output switch group with the clock signal.

CONSTITUTION: An optional function waveform is supplied through the input terminal IN, and the ON/OFF is controlled for switch groups wSW1WwSWn by the value obtained by decoding the clock CP(a) through the decoder 1. Then the waveheight value of the optional function waveform at an optional time point is stored in the capacitors C1WCn. Then the ON/OFF is controlled for the switch groups rSW1WrSWn by the value obtained by decoding the clock CP(b) having a different frequency from the clock CP(a) through the decoder 2. And the waveheight values stored in capacitors C1WCn are delivered successively to the output terminal OUT. Thus an optional function waveform having a different repetitive frequency from the input optional function waveform can be obtained at the terminal OUT. Accordingly the respective frequency can be altered for the optional function waveform with a simple constitution of circuit.