An automatic player piano is equipped with a preliminary data producer comprising an experimental routine and an editor; a motion controller forces each of the black and white keys to travel on a test trajectory at different values of key velocity so that the black or white key gives rise to rotation of hammer by means of an action unit, and a hammer sensor varies the magnitude of a hammer position signal depending upon the current hammer position; the hammer velocity is converted to a value of MIDI velocity so that a table producer correlates the values of key velocity with the values of MIDI velocity; while an automatic player is performing a music passage, the motion controller exactly determines a value of key velocity on the basis of the relation already determined by the preliminary data producer.