Each of Dampers provided for each of keys is controlled in response to both an operation of a damper pedal and an operation of the corresponding key. For each of the dampers and over one stroke of the pedal in at least one of depressing releasing directions of the pedal, load information indicative of loads imposed on a portion linked to the damper is acquired in association with individual stroke positions of the pedal. Then, for each of the dampers, a half pedal region is identified on the basis of relationship between the stroke positions and the loads corresponding to the stroke positions. The portion linked to the damper may be any suitable portion related to a damper lever moving in an up-down direction in interlocked relation to both of vertical movement of a lifting rail responsive to an operation of the pedal and an operation of the key.