Abstract: Data to be used for generating tone waveform data corresponding to a partial time section of a tone are stored in a basic file or expansion file. In a wave part area of each of the files, there are stored wave part data to be used for generating tone waveform data corresponding to a partial time section of a tone, and the wave part data includes information designating several groups of template data indicative of variations, in the partial time section, of a plurality of tone factors, such as a waveform template, pitch template, amplitude template, spectrum template and time template. Each of the expansion files contains data representative of differences from data stored in the corresponding basic file. The data are stored in such a manner as to avoid overlapping data storage, in order to minimize the total quantity of data.