To cope with both a case wherein severe sound effects are requested and a case wherein sound effects need not be severe so much by adding the sound effects by the same operating program irrelevantly to which of a high- precision sine wave and a triangular wave a basic wave is.

A panel operation element 10 has an operation element (for selecting a sign wave or triangular wave) so as to select an added effect sound. A ROM 60 stores the program for operating a CPU 70 and also stores programs corresponding respective effects for operating a digital signal processor(DSP) 90 and a coefficient determined according to which of the sine wave and triangular wave the basic wave is. This device varies the input from an input means to make difference a coefficient supplied to a coefficient RAM of the DSP 90, and a choice between the case wherein a modulated signal is based upon a high-precision sine wave and the case wherein it is based upon the triangular wave is made without changing the program of the DSP 90.