Key is pivotably supported by a key frame, and the front end of the key is normally urged upward by a pivot lever. Load member drivable by an actuator is provided rearwardly of a mass body of the pivot lever. Key switch and proximity sensor detect a pivoting position of the key responsive to depression and release operation of the key. Load control circuit performs driving control of the actuator, in accordance with the pivoting position of the key, to move the load member back and forth, to thereby cause the load member to engage (or contact) with the mass body in a depression stroke and terminates the engagement in a release stroke.