A transmission mechanism includes a plurality of drive gears disposed on a counter shaft and a plurality of driven gears disposed on a drive shaft. Each of the plurality of drive gears is engaged with each of the plurality of driven gears to form a plurality of shift-gear pairs. An eight-speed drive gear, which forms an eight-speed shift-gear pair having the smallest reduction gear ratio, and a seven-speed drive gear, which forms a seven-speed shift-gear pair having the second smallest reduction gear ratio, are disposed adjacent one another at a center portion of an arrangement of the drive gears. An eight-speed driven gear, which forms the eight-speed shift-gear pair, and a seven-speed driven gear, which forms the seven-speed shift-gear pair, are disposed adjacent one another at a center portion of an arrangement of the driven gears.