PURPOSE: To simplify constitution of the speed change operation mechanism by constituting the speed change operation mechanism out of a shift shaft and a plurality of forks provided on this, and providing a means to energizate the shift shaft to a neutral position between a transmission case and both ends of the shift shaft.

CONSTITUTION: In the transmission case 4 of a manual transmission 2, the shift shaft 14 for speed change gear trains of a speed change operation mechanism is arranged, for selectively engaging a first speed gear train - a fourth speed gear train. The speed change operation mechanism is constituted out of the shift shaft 14 for speed change gear trains and a plurality of forks 22, 26 arranged on it. Between the transmission case 4 and both ends of the shift shaft 14, an energizating means 16 to energizate the shift shaft 14 to a neutral position is arranged. According to movement of a shift and select shaft 18 by shift operation of a shift lever, a shift and select lever 20 is moved in the axial direction and in the circumferential direction, to selectively engage respective gear trains.