Once performance event information is supplied in real time in accordance with a progression of a performance, a time indicative of temporal relationship between at least two notes to be generated in succession is measured on the basis of the performance event information supplied in real time. Comparison is made between a preset rendition style determination condition including time information and the measured time, and a rendition style that is to be applied to a current tone to be performed in real time is determined on the basis of the comparison result. With the arrangement that a rendition style to be applied to the current tone is determined on the basis of the comparison result, it is possible to execute a real-time performance while automatically expressing a tonguing rendition style.