A new steering control method for wheel systems of agricultural machinery to enhance the follow-up performance with a tractor was developed to improve the operability of semitrailed agricultural machinery. The basic concept of this control method is the alignment of the turning radius of tractor and machine for a constant turn, and a formula was derived for expressing this geometrical relationship. Based on this formula, a control method was developed which uses the steering angle of the wheel system of an agricultural machine as a variable for the steering angle of the tractor’s front wheels and the angle of traction. Thereafter, this control method was applied to the in-line type prototype test trailer and a commercially available roll baler and running tests were conducted. The results showed a significant improvement in the follow-up performance of the trailer and roll baler attached to the tractor. However, since the need to measure the steering angle of the tractor’s front wheels is difficult for practical application, the steering angle of the tractor’s front wheels was estimated and the estimated values were used for the control for application to the commercially available roll baler. The results of this test showed that the same level of follow-up performance could be achieved as when the steering angle measured for the tractor’s front wheels was used and that applications were possible. It was also confirmed that by the addition of a compensation coefficient for a slope to the estimated figures, a high follow-up performance could be achieved even on sloped grassland.