PURPOSE: To improve expression force of automatic playing by fuzzy-inferring automatic playing information given in a style such as MIDI format.

CONSTITUTION: Based on an input event line, the corrected values of the timing and the force of key depression are inferred by a fuzzy inference means from the CPU in a key drive unit 13. The event line comprises on-velocity, gate time, interval time, and the like, input based on a MIDI format for example. Based on the event line, the way how is the playing means is inferred, and the timing or the force is corrected corresponding to the inference. For example when it is judged to be playing of staccato, the key 3 is strongly driven only in a short time. Further, in the case of repeated depression before the key 3 is returned, next key drive is begun in OFF of the key. By such instruction, based on automatic playing data recorded with a simple format, automatic performance having the expression force near to actual performance can be performed.