Performance event data designating rendition style modules are supplied in order of time. When a given performance event data at a given time is to be processed in accordance with the supplied performance event data, another performance event data related to one or more events, following the given performance event data, is obtained in advance of a predetermined original time position of the other performance event daata. Control data corresponding to a rendition style module designated by at least one of the given performance event data and the other performance event data obtained in advance is generated on the basis of the given and the other performance event data, and a waveform corresponding to the designated rendition style module is synthesized on the basis of the control data. Characteristic of at least one of preceding and succeeding rendition style modules is modified on the basis of trailing end information of the preceding rendition style module and leading end information of the succeeding rendition style module. When rendition style designation data, including information designating a rendition style module and parameters for controlling the rendition style module, is lacking in a necessary parameter, the lacking parameter is filled with a predetermined standard parameter.