To ensure lubricity of a rotation supporting part of a reverse free rotating gear, while possessing the advantage of an output reduction gear type, and to determine the setting of lower intensity/rigidity of a counter shaft and its supporting part.
An output reduction gear type of a transmission gearbox includes prescribed pairs of transmission gears 1G,..., 6G corresponding to a selected transmission stage. In these pairs of transmission gears 1G,..., 6G, a power transmission switching mechanism is operated to change a power transmission route so as to transmit power from an input shaft Si to an output shaft So directly or through a counter shaft Sc. The power transmission switching mechanism is provided with three synchromesh devices Ya,..., Yc, which are entirely disposed on the input shaft Si. Each of gears on the input shaft Si is provided rotatably relative to the input shaft Si, and a pair of the backward gears 6G are arranged in closer proximity to the input shaft Si than the remaining pairs of transmission gears 1G,..., 5G.
KAMEDA OSAMU
SAKAMOTO KENJI
