The present invention is capable of suppressing gear shift shocks or delays in acceleration with no interruption of driving force and reducing the weight. Disclosed is a transmission which is provided with multiple stage shift gears 19, 21 so arranged to shift a number of dog clutches 47, 49 to shift a gear to the upper stage of the multiple stage shift gears 19, 21, and is characterized in that a guide part G is provided to a shift operation section 93 and the dog clutches 47, 49 on each of the sages so as to move the lower dog clutch 47 in a neutral direction by a coasting torque acting on the lower stage by a shift rotation of the upper stage to release a meshing engagement when meshing engagements of the lower and upper dog clutches 47, 49 are simultaneously performed by an operation of the shift operation section 93.