Tone generator LSI generates a subframe start signal to be interruptively given to a microprogram, by which the microprogram is activated to issue an interrupt signal to a device driver. In response to the interrupt signal, the device driver prepares control data for use in a next frame. The microprogram receives control data from a RAM at the beginning of each frame and calculates control data for individual samples of the frame on the basis of the received control data as well as control data generated for the last sample of an immediately preceding frame, so as to create a plurality of samples of tone data for each subframe. The thus-created tone data are temporarily written into a buffer and then read out from the buffer in accordance with predetermined clock pulses.