Abstract: A control device controls the draft for moving the working machine, such as a plow, up or down. The working machine is mounted on a tractor by way of a hydraulic lifting device which is adjusted to the tilling depth predetermined by a tilling depth setter which depends on the increase or decrease of traction resistance detected by a draft sensor. When the lifting machine is changed from the ascending position to the descending position, the draft control function is stopped for a specified short time or a specified short distance to lower the working machine quickly. However, the quick lowering of the working machine is inhibited when the relationship between the detected value by the draft sensor and the preset value by the tilling depth setter is not at the descending position of the working machine.