A servo controller of an automatic player piano normalizes an actual key position to a value less than a reference value indicative of a target stop on a reference trajectory when the key is found in a region immediately before the target stop and to another value greater than the reference value when the key exceeds the target stop, and adjusts a driving signal to a proper value in such a manner that a solenoid-operated key actuator minimizes the difference between the value or another value and the reference value, whereby the servo controller keeps the key in a narrow region on both sides of the target stop for reproducing stop-and-go key motion.