Technology is provided that contributes to an improvement in the ease of assembly of transmissions. A fork mechanism (20) is configured in which fork rods (FS1, FS2, and FS3) to which shift forks (F1, F2, and F3) are connected are each attached to a pedestal (22) so as to be moveable in an axial direction. An assembly guide portion (30) is provided on the pedestal (22) and a guide pin (19) is erected on a clutch housing (12). As a result, even in cases where an input shaft (2) and a main shaft (4), on which driving and driven gears and synchro devices are assembled, are assembled on the clutch housing (12) in a state that the driving and driven gears are engaged and, thereafter the fork mechanism (20) is assembled on this clutch housing (12), the assembly of the fork mechanism (20) on the clutch housing (12) can be easily performed.