A key depression (i.e., string striking) is performed while a pedal is kept at a set non-key-depressed-state corresponding position (a rest position of a hammer). A string striking velocity immediately before string striking and a string releasing velocity immediately after the string striking are detected, and a coefficient of rebound is calculated on the basis of the detected velocities and stored in association with the current value of the rest position of the hammer. Similar operations are repetitively performed with individual ones of different rest positions of the hammer, wherein each of the different rest positions of the hammer corresponding to each of a plurality of stroke positions within one stroke of the pedal. Thus, a distribution curve of the coefficients of rebound detected in association with the plurality of stroke positions is obtained and a half point of the pedal is identified based on the distribution curve.