PURPOSE: To lessen the fatigue of a threshing worker sitting on a seat by making a driver's seat in such a manner as to be changeable between the forward driving posture and the backward working posture.

CONSTITUTION: The seat 16 is composed of a backrest 16a, a sitting part 16b and a foot guide 16c and the right lower end of the sitting part 16b is connected to the upper right end of an engine bonnet 18 in a state rotatable around a longitudinal shaft P3. When the seat 16 is turned outside, it rotates by about 180° until the left side face 19 of the backrest 16a is brought into contact with a side face 18a of the engine bonnet 18. In the above state, the backrest 16a acts as the foot guide and the foot guide 16c acts as the backrest 16a and the driver can sit backward in a state opposite to a feeding table 17 using the back face of the sitting part 16b.