To prevent an oil from spouting out from an air vent hole in an oiling plug even when a bevel gear stored in a gear case is rotated at a high speed in cultivation.

An axially supporting part of a bearing 22 is located at a little center part than the left side part 3c of a gear case 3 to install a vacant room 3b for attaching the oiling plug 23 between the base part of a left arm 11 and the bearing 22 and the oiling plug 23 is attached on the vacant room 3b in a state that the oiling plug 23 is not projected from the top face 3d of the gear case 3 in the gear case 3 configured by extendedly installing arms 11 and 13 in the right and left directions of the gear case 3 set at the center of the machine, axially supporting an input shaft 16 in the back and forth direction of the gear case 3, fixedly installing a pinion bevel gear 19 at the point thereof and axially supporting a driving shaft 21 in which the bevel gear 20 engaged with the pinion bevel gear 19 is fixedly installed at the left side of the input shaft 16 with a bearing 22.