PURPOSE: To reduce trouble such as pushing down of planted grain culms or occurrence of residual unreaped grain culms by operating either or both of a moving means and a steering means according to the extent of positional deviation of a reaping part.

CONSTITUTION: Positional deviation is sensed in plural stages by a means (S2) for sensing the positional deviation of a reaping part. When the positional deviation is small, either of an electrically operated motor 20 and a control valve 27 is operated. When the positional deviation is great, both of the control valve 27 and the electrically operated motor 20 are operated. The reaping part is moved by the electrically operated motor 20 and a car body is steered by the control valve 27.