Abstract: Reading of a waveform memory is controlled and one of different processing is performed depending upon which of a first mode and a second mode has been designated. When the first mode has been designated, an interpolation operation is performed on the basis of plural sample value data read from the waveform memory by using a predetermined number of processing time slots and a resulting one waveform sample value data is produced. When the second mode, has been designated, a processing for producing one waveform sample value data is performed on the basis of one sample value data read from the waveform memory by using one processing time slot. By using a predetermined plural number of processing time slots, one waveform sample value data produced with a high accuracy in the first mode whereas plural waveform sample value data are produced in the second mode whereby generation of a waveform can be performed efficiently by properly utilizing the mode.