PURPOSE: To improve turning properties and stabilize traveling of combine by constructing car body to be able to move in rolling by respectively providing cylinders for rolling in both of slide crawler and fixed crawler, or in either of the two.

CONSTITUTION: Stroke value detected by stroke sensor goes over a stroke set value set by a stroke-difference setting device for a case of crawler 1 is not able to lower more in wet field working. Said state is judged by the stroke- difference setting device and cylinder 34 for slide is elongated to slide the slide crawler 1. A distance between crawler 1 positioning outside of depressed part and fixed crawler 14 is widen and weight balance of left and right is corrected, then sinking amount of the slide crawler 1 is decreased. Thus, the slide crawler 1 is able to be moved upward and a room to re-lower arises, then rolling control is able to be revived again.