PURPOSE: To prevent an agricultural machine from being quickly turned at the second state in the case of such an agricultural machine as being turned by disconnecting a clutch at the first stage and actuating a brake at the second stage, by allowing the actuator to have a definite difference in resistance between the first and second stages.

CONSTITUTION: For example, when an actuating lever 3 is slanted left against a spring 8, a microswtich 11 is turned on by the slanting of a disk 7 at the lower end of a lever 3 and a clutch 17 in the left wheel running driving shaft is disconnected through a cylinder 14 by the actuation of a solenoid valve 1. Thus, a machine body is turned left. Then, when a quick turn of the machine body is required, the lever 3 is slanted against a spring 16 with larger force than that of the spring 8 and a valve 12 is slid downward and then a brake device 15 at the left wheel side is actuated. Since the clutch 17 has already been disconnected in this state, the left wheel can fully be stopped and the machine body can be turned quickly only by revolution of the right wheel.