To prevent an electric motor from being corotated and becoming high temperature due to heat generation in a transmission device equipped with the electric motor as an auxiliary power or the like.

The transmission device is constituted where a plurality of pairs of change gears 15a , 15b to 19a, 19b which are provided between an input shaft 12 connected to an internal combustion engine 10 and a spindle 13 connected to driving wheels 39a, 39b, and engaged each other are selectively switched so that the power transmission between both shafts performed by either pair of them, the driving wheel is driven by the electric motor 30 through an interlocking mechanism 31 in addition to the internal combustion engine, and the power transmission between the electric motor and the driving wheel is shut off in such a state that the pair of change gears to be the maximum speed stage is selected. A driven side change gear 19b of the pair of the maximum speed stage and the last rotary member 31c of the interlocking mechanism can be rotatably provided with the spindle by being abutted each other, and selectively connected to the spindle by the maximum speed stage switching sleeve 22a slidably provided in the axial direction.