PURPOSE: To realize the optional waveform generator able to give a minute phase change less than a clock period to one waveform in the optional waveform generator able to obtain a required waveform through waveform addition.

CONSTITUTION: The optional waveform generator of waveform addition type provided with plural memory sections 1a, 1b storing a waveform data as a digital data, plural D/A converters 2a, 2b D/A-converting the waveform data of the memory sections 1a, 1b, a clock generating section 3 generating a clock to be applied to the memory sections 1a, 1b and the D/A converters 2a, 2b and an adder 8 adding plural waveforms is provided with a delay means 9 delaying the clock given to any of the memory sections 1a, 1b and the D/A converters 2a, 2b.