To remotely operate a tricycle tractor of special structure by controlling a motor for steering and an actuator for slider to be operated during the manual operation so that the difference in the quantity of the light reception of a reflection surface sensor on each side of a base part is kept in an approximately same level.

A light reflecting tape 40 of the prescribed width is attached to a track of a tricycle tractor 9. Reflection surface sensors 31, 32 to irradiate the light on the light reflecting tape 40 and receive the reflected light are provided on each side of a tip part of a base 1, and a reflection surface sensor 33 is provided in the middle position. An ultrasonic sensor 37 to detect an obstacle ahead is provided forward. When a front wheel 2 is deviated aside from the light reflecting tape 40 during the automatic operation, the level of the detected signal of the reflection surface sensor 31 or 32 on the deviation side is dropped. A body 7 is moved to the reflection surface sensor 32 or 31 side in an opposite manner. The front wheel 2 travels on the light reflecting tape while the automatic balanced condition so that each detected signal is approximately in the same level in a motor control means 26 for steering.