A position information acquisition unit (62) acquires position information for a robot tractor (1) that autonomously travels along a predetermined travel route, and position information for a manned tractor (1X) that travels on the trailing side of the robot tractor (1) and that performs work in coordination with the robot tractor (1). A separation distance specification unit (63) specifies the separation distance between the robot tractor (1) and the manned tractor (1X). An emergency stopping unit (65) stops an engine of the robot tractor (1) when the separation distance exceeds a first threshold value and causes the robot tractor (1) to perform an emergency stop. A separation distance adjustment unit (66) temporarily stops the robot tractor (1) without stopping the engine or causes the robot tractor (1) to decelerate, when the separation distance has not exceeded the first threshold value and is equal to or greater than a second threshold value that is smaller than the first threshold value.
