Abstract: A transmission mechanism having a PTO transmission system and a traveling transmission system and used for a working vehicle, which is so constructed that a input shaft 8 is coaxially freely perforated through a hollow traveling clutch shaft 13, both ends of input shaft 8 projects from the traveling clutch shaft 13, one projecting portion is journalled between a bearing wall 1b of a front transmission casing 1 and a front bearing plate 4 for covering an opening at the front end of the wall 1b, and a selecting device A including a forward and rearward movement switching clutch B, as an embodiment of an auxiliary speed change device, is disposed at this projecting portion.