An address for reading, from a waveform memory connected by a bus, waveform data to be assigned to each of a plurality of sound generation channels for generating a musical sound, is calculated, by time division, for each sound generation channel, and the calculated address and the sound generation channels are associated and stored in an address memory. When the bus is in an empty state, an address stored in the address memory is read, and waveform data is read from the waveform memory based on the read address; the read waveform data is assigned to the corresponding sound generation channel, and generation of a musical sound is prescribed for the sound generation channel to which the waveform data is assigned.