A transmission includes a fork mechanism in which a plurality of fork rods to which a plurality of shift forks are connected are each attached to a pedestal so as to be moveable in an axial direction. An assembly guide portion is disposed on the pedestal and a guide pin is erected on a clutch housing. As a result, even in cases where an input shaft and a main shaft, on which driving and driven gears and synchro devices are assembled, are assembled on the clutch housing in a state that the driving and driven gears are engaged and, thereafter the fork mechanism is assembled on this clutch housing, the assembly of the fork mechanism on the clutch housing can be easily performed.