A musical tone control apparatus having first and second detecting means (30R, 30H) mounted on a player's arm for detecting bending angles of player's joints, a musical tone control data generating means (29) worn on the player's waist for generating musical tone control data based on output signals of the first and second detecting means (30R, 30H). The musical tone control data generating means (29) is connected to the first detecting means (30R) via the second detecting means (30H) through a single common cable (i.e. transmitting means). Hence, the number of common cables (i.e. the number of transmitting means) can be reduced to the minimum, allowing free movement of the player. Further, the first detecting means (30R) having a potentiometer comprises first and second links rotatably connected at their ends so that the links rotate in a bending direction of the player's joint, a resistance element provided at the first link, and a sliding contact provided at the second link. The sliding contact, keeping contact with the resistance element, slides thereon with the rotation of the first or second link. The potentiometer produces a signal between the sliding contact and the terminal of the resistance element in response to a bending angle of the player's joint. Hence, the detecting means can be made thin, allowing free motion of the player's arm.