PURPOSE: To connect two clutches smoothly at the time of connecting each gear to an input shaft and an output side shaft freely to disconnect by engaging a synchronous engagement type clutch after engaging a dog clutch.

CONSTITUTION: When a shift fork 16 is moved to the right side, a first clutch 40 is engaged, and a second clutch 50 is engaged with a reverse gear device side. As a result a reverse input gear 6 is locked with a counter shaft 3, and a reverse output gear 7 is locked with a main shaft 2 to transmit the power reversely. At this stage, since a reverse side clearance of a synchronizer key 21 is larger than a clearance between a sleeve 15 and a reverse output gear side gear spline 10, the first clutch 40 forming a dog clutch is engaged before, and after the engagement of a gear spline 15a and the gear spline 10, the synchronous engagement type second clutch 50 is engaged. Smooth engagement is thereby performed.