PURPOSE: To perform the support of a steering handle so simply and securely by installing plural numbers of clamp bearing surfaces in a handle bracket supporting a handle frame horizontally and turnably, in an upper end of a transmission case.

CONSTITUTION: When a steering handle 3 is operated up and down, a transmission case 2 is longitudinally rotated around a travel shaft from an upper side plate 17 via both symmetrical side plates 13, a clamp bearing surface 6 and a bolt 14 together with via a handle frame 4, a rotating plate 21, the upper side plate 17, a pinch plate, the clamp bearing surface 6 and a bolt 23. When an operating lever 28 is rotated upward and an engaged device 26 is separated from a notch 18 of the upper side plate 17, the handle frame 4 is rotated left and right around a guide disk 19 together with the rotating plate 21. On the other hand, when the operating lever 28 is rotated downward, the handle frame 4 is locked to a handle bracket 5.