PURPOSE: To eliminate the useless work to reap an already reaped field and to prevent unnecessary meandering motion of a combine, by changing the range to correct the machine body toward the left side in the side reaping operation according to the deviation of the moving direction of the machine body from the standard direction of the former reaping operation.

CONSTITUTION: Round-about reaping operation is carried out while measuring the standard direction A of the machine body in the side-reaping edge with a direction sensor. In the above operation, the correction range of the machine body toward the left direction is changed according to the difference between the moving direction B of the machine body and the former standard direction A. The direction B of the machine body entered into the side-reaping position is compared with the standard direction A of the former side-reaping site. When the entering direction B is shifted rightward, the correction range C is widened and when it is shifted leftward, the correction range C is narrowed.