A keyboard apparatus having a construction which can maintain an excellent balance in touch feeling between white keys and black keys and can be made compact in size in the longitudinal direction. The driven part of each of mass bodies associated with respective white keys and the driven part of each of mass bodies associated with respective black keys are at the same longitudinal location, and at the same time the distance between the driven part of each black key-associated mass body and a pivotal motion support associated therewith is longer than the distance between the driven part of each white key-associated mass body and a pivotal motion support associated therewith.