An upright keyboard instrument comprises a prescribed number of keys that are interlocked with actions, hammer assemblies, and a plate spring unit, which is interlocked with a loud pedal. When the key is depressed, the action is activated to drive the hammer assembly, thus producing a musical tone. Each of plate springs is normally arranged close to an end portion of a whippen included in the action. Upon depression of the key, the end portion of the whippen comes in contact with the plate spring to cause a resistive force, which is transmitted back to a player's finger depressing the key. When the loud pedal is depressed, the plate spring departs from the end portion of the whippen, which becomes free to rotate upon depression of the key, thus realizing loudness effect on sound.