PURPOSE: To simplify construction of the aimed device and prevent operation error by providing a power take-off clutch for turning power take-off transmission from an input shaft to a power take off part to off while interlocking with transfer to neutral position of gear change key in a speed change shaft.

CONSTITUTION: Transmission from an input shaft 1 to a power take-off part 6 is turned on or off through a power take-off clutch 7 on a speed change shaft 3 to transmit power always in a definite transmission ratio regardless of position of speed change transmission by a speed change key 5. Since the power take-off clutch 7 is operated to turn-off position by operating the speed change 5 key from speed change position to neutral position N, transmission from the power take-off part 6 to a working machine is not carried out when running transmission is in neutral position. Further, the construction of the aimed device is also simplified and the device is free from operation error, since the speed change key 5 operates the power take-off clutch 7 together with gear change.