Upon activation by a power-on operation, a CPU transfers part of waveform data items of predetermined tone colors from a waveform data storage to a waveform RAM, and after this, transfers data items including the remaining waveform data to be transferred. Thereby, a musical sound generating device assigns the transferred waveform data items to make it playable when the transfer of the part of the waveform data has been completed, and changes the assignment of the waveform data to make it playable in an ordinary state when the transfer of the remaining waveform data has been terminated.