To reduce the deflection of a shift fork due to operating physical force and so on required for synchronization so as to smoothly execute shift operation by arranging shift rods on the sides of an input shaft and a countershaft and also in a range between the center shafts.

Shift rods 63-65 are required to be arranged in the side direction of an input shaft 3 and a countershaft 4 in view of such a layout condition that an inversion mechanism is arranged above the input shaft 3, a 5-R shift synchronizing device 18 and a 1-2 shift synchronizing device are arranged on the countershaft side, and a 3-4 shift synchronizing device is arranged on the input shaft side. Besides, the shift rods 63-65 are arranged on the sides of the input shaft 3 and the counter shaft 4, and also arranged in a range of D between center shafts of each shafts.