An upright piano includes action units between keys and hammers, and the action units are less prompt so that a missing tone tends to take place in a music passage through high-speed repetition; the action unit is constructed from a whippen assembly, a jack mechanism provided on the whippen assembly and a regulating button mechanism for an escape in cooperation with the jack mechanism, and a compression coil spring is provided between a center rail and the whippen assembly for urging the whippen assembly in a direction toward the original position, thereby accelerating the restoration of jack to the contact with the hammer.