PURPOSE: To control an agricultural traction type working machine, rotatably installed through a traction device in the horizontal direction in the rear of a tractor and designed to perform the operation at a position just after the tractor so as to follow and travel after the tractor.

CONSTITUTION: A folding angle (θ) at a traction point 2 where an agricultural traction type working machine (baler) 3 is connected to a tractor 1 is sensed with an angle sensor and travel wheels 7 of the working machine 3 are subjected to steering control based on the sensed folding angle of the traction point and a change thereof (μ') per time so that the travel loci of one optional point (A), located between front wheels 4 and rear wheels 5 of the tractor 1 and situated on the center line (C) of the car body on a planar projection drawing of the tractor 1 and one optional point (B) located on the center line (C) of the car body on the planar projection drawing on the agricultural traction type working machine 3 may coincide.