PURPOSE: To enable proper conversion effectively by forming a transmission gear integrated with a first input shaft, installing the transmission gear, etc., on a power transmission shaft, PTO input shaft and a second PTO power transmission shaft, and coupling the PTO input shaft with first PTO power transmission shaft.

CONSTITUTION: When a forward-reverse shift lever is put in the forward position and a main shift lever is turned to the first speed position, a hub sleeve 12 on the forward input shaft 10 of a main transmission 1 meshes with a transmissive gear 14, and a forward-reverse selecting hub sleeve 16 on a main transmission output shaft 11 is put in synchronous meshing with a transmission gear 17, while a hub sleeve 20 on a PTO input shaft 18 meshes with a transmission gear 21. When an aux. shift lever is turned into the first position, a hub sleeve 26 on a guide shaft 50 of an aux. speed-reducing transmission 2 and a hub sleeve 47 on a running output shaft 46 mesh with transmission gears 27 and 48, and the first forward speed is established. Through similar lever operations, the running output and PTO output of fifteen forward positions and nine reverse positions are extracted, and the output shaft 46 transmits the running power while PTO output shaft 44 drives a working machine.