To make an assembling property for a bracket excellent, to reduce working manday, and to attain downsizing.

A reverse shift arm 43 is swung to a reverse direction by operating a shift head 35 fixed to a 5th shift position-reverse fork shaft 32 to the reverse direction, and an astern position is established by shifting a reverse idler gear to a reverse meshing position by the arm 43. Both end parts of a reverse shift arm bracket 42 are insertedly supported by the first and second reamer bolts 40, 41 fixed to a transmission case in a direction orthogonal to the fork shaft 32. The reverse shift arm 43 is supported by the first reamer bolt 40, and a 5th shift position shift arm 47 is supported by the second reamer bolt 41, freely to be oscillated respectively. One end part of the arm 47 is engaged with a 5th shift position shaft attached with a 5th shift position shift fork 48, and the other end part is engaged with the shift head 35.