PROBLEM TO BE SOLVED: To prevent the quick return from a halt working state at a levee side to a traveling work state, decreasing the risk of careless quick start and improve safety while arbitrarily controlling the turning radius by differing the driving speeds of the right and left crawlers 2, 2 with a differential gear mechanism 45.SOLUTION: Right and left side clutches (38R, 38L) a straight motion clutch (51) and a turning clutch (52) are switched to a transmission blocking state based on the operation of a raking operation tool (18) arranged at an operation unit (3), and the right and left side clutches (38R, 38L) and the straight motion clutch (51) are switched to a transmission connecting state based on the returning operation of the raking operation tool (18) only when the main speed change lever (15) is operated to a neutral position or a low-speed range near the neutral position.COPYRIGHT: (C)2009,JPO&INPIT【課題】差動歯車機構45を介して左右の走行クローラ2,2の駆動速度を異ならせて旋回半径を任意に調節することができるものでありながら、畦際での停車作業状態から走行作業状態への高速での復帰を防止し、不用意な急発進を少なくして安全性を向上させる。【解決手段】操縦部(3)に設けた掻込操作具(18)の操作に基づいて左右のサイドクラッチ(38L,38R)と直進クラッチ(51)及び旋回クラッチ(52)を伝動遮断状態に切り換え、主変速レバー(15)を中立位置あるいは中立位置に近い低速域に操作した状態でのみ、前記掻込操作具(18)の戻し操作に基づいて左右のサイドクラッチ(38L,38R)と直進クラッチ(51)とが伝動接続状態に切り換わる構成とする。【選択図】図7
