PURPOSE: To permit an operating lever to rotate singly so as to enhance operability of a mechanical assisting device for the operating device of a gear transmission having a selecting control shaft by providing two articulated members between a transmitting member and the switching control shaft, with a spring interposed between the two members.

CONSTITUTION: This mechanical assisting device 10 attached to the operating device of a gear transmission comprises a rotating lever 8 provided at one end with a spherical part 7 to which a cable having one end connected to an operating lever is connected at the other end, and a small plate 9 pivotally mounted thereon by an articulation shaft 13, and the switching control shaft of the gear transmission is attached to a cylindrical member 11 secured to the small plate 9. When the operating lever is operated, the small plate 9 and the rotating lever 8 rotate against a spring 20 until a sleeve and a synchronous ring in the gear transmission mesh with each other. In this case, the rotational angles of the small plate 9 and the rotating lever 8 are reduced by the stored force of the spring 20, and after the sleeve is propelled in the direction of an input shaft gear and the gear transmission is synchronized, the sleeve and the synchronous ring are brought in mesh with each other.