A player changes the pitch of tones produced through a trombone by controlling the breath and a slide, and the control of slide is not easy for children, handicapped persons and old players; a supporting system is combined with the trombone, and includes a manipulating board fitted to an appropriate portion of the trombone close to the slide, a driving mechanism connected to the slide and a controlling unit connected to the manipulating board and driving mechanism; when the player wishes to change the pitch of tones through the sliding motion of the slide, he moves a lever on the manipulating board by a distance shorter than a target stroke of the slide, and the controlling unit calculates the target stroke so as to supply a driving signal to the driving mechanism; and the driving mechanism exerts force on the slide so as to assist the player in varying the length of the column of air.