PURPOSE: To permit the linking of the main clutch ON-OFF operation necessary for changing speed with the operation of a lever by allowing a main clutch to be cut automatically according to the movement of the speed change lever in lever changing operation and to be turned-ON automatically after lever changing operation.

CONSTITUTION: The other end of the inner wire 25 of a release wire 24 which is linked with the cam operating piece 4 of a main clutch 2 is connected with a second swing body 23 so that the cam operating piece 4 is in operation situation when the second swing body 23 is in the first situation, and the outer wire of the release wire 24 is divided into two parts, and one divided wire 26 is connected with a first swing body 20 so that the cam operating piece 4 is inoperative situation when the first swing body 20 is in the first situation, and the cam operating piece is in operation situation when the first swing body 20 is in the second situation. Thus, the main- clutch 2 is automatically ON-OFF operated by a speed change lever 3.