PURPOSE: To prevent tear etc. of grass due to wheel peripheral speed becoming slower than actual wheel movement resulting from the peripheral speed difference between the front and rear wheels and the inner and outer wheels by interposing a center differential mechanism, which distributes power to front and rear wheels, on a transmission shaft installed in parallel with the output shaft of a main transmission device.

CONSTITUTION: In a four-wheel driven tractor, the front and rear wheels are driven by further performing high/low aux. transmission in a transmission case M after the engine rotation is subjected to forward/reverse continuously variable transmission by a transmissive HST type transmission device H. The front end of an output shaft 2 of the transmission device H trotrudes in the transmis sion case M, and an aux. transmission shaft 3 is engagingly to the front end of this output shaft 2. A front differential case cylindrical shaft 8a is furnished in parallel with this output shaft 2 as transmission shaft facing against the aux. transmission shaft 3, and a center differential mechanism D is interposed in this cylindrical shaft 8a. This mechanism D transmits distributedly the power to a rear wheel drive shaft 4 and a front wheel drive shaft 5.