To prevent occurrence of abnormal noise or shock at the time of "C/L gear thrusting-aside" resulting from the torsion of a synchronized side in a variable speed gear including a gear shift actuator which actuates a gear shift mechanism of a synchromesh transmission.

A means for positively increasing the speed of advance of a sleeve of a synchronization mechanism until it rides over a synchronization ring and then makes contact with a clutch gear, an orifice 27 is additionally provided in an oil damper 17 including an orifice 25 at stroke ends of pistons 22a, 22b, the orifice 25 being adapted for throttling the flow of oil accompanying the strokes of the pistons interlocked with the shift action of the gear shift actuator. The orifice 27 is opened until the piston 22a or 22b enters the stroke end region, and is closed by the piston 22a or 22b until the piston reaches the stroke end after it has entered the stroke end region.