PURPOSE: To adjust tread width of a farmwork vehicle in a designated value by sliding an axle and inserting the one end portion into a shaft hole of one side of a housing and attaching a wheel to the other protruded end portion by a wheel attaching tool.

CONSTITUTION: An axle 5 fit in a key boss 1 of a gear 2 in a slidable manner is inserted into shaft holes 3a, 3b of a housing 4 and a drive wheel 6 is detachably attached to this axle 5 through a wheel attaching tool 7. The axle 5 includes a long key groove 12 for a guide key 10 and pin insertion holes 13a, 13b and the wheel attaching tool 7 is formed by a cylindrical portion 17 where a pin pressing hole 16 is formed and a flange for attaching a wheel 14 of the drive wheel 6. For example, when an end portion 5a of the wheel 5 is inserted into the shaft hole 3a of the housing 4, the other end portion 5b is protruded from the shaft hole 3b and the cylindrical portion 17 of the wheel attaching tool 7 is attached hereto. Thereby, the wheel can be attached optionally to either one end of the axle 5 through the wheel attaching tool 7 and the tread of left and right wheels of a farmwork vehicle can be determined in a designated width.