PURPOSE: To prevent unnecessary move of a shift rod and a shift fork for advancing in establishing a backward stage by providing a transmission mechanism for advancing in which only motion of a shift member between a neutral position and an advancing extablishing position is transmitted between the shift member and the shift rod.

CONSTITUTION: In a shift mechanism comprising a shift fork 51 for advancing for establishing an advancing gear line in accordance with move of a shift member 48 from a neutral position to an advance side establishing position fixed on a shift rod 63, a transmission mechanism 661 for advancing is provided for transmitting motion of the shift member 48 between the neutral position and the advancing establishing position to the shift rod 63 only. This transmission mechanism 661 for advancing is provided with an engagement part 48b to be provided at the shift member 48, and a cam lever 671 which can be oscillated in accordance with move of the shift member 48 and which is connected to the shift member 48. The cam lever 671 is formed provided with a returning can 72 for converting the motion of the shift member 48 into axial move of the shift rod 63 by oscillation actuation at the time.