To reduce the probability of collision due to the matching of reception/ transmission periods by repeating reception and transmission while differentiating the time at random when a self-traveling vehicle enters a section provided with the possibility of the collision and confirming the presence of the other vehicle.

When the self-traveling vehicle A traveling in the yard of a plant or the like enters the section (intersection area) 2 provided with the possibility of colliding with the other self-traveling vehicle B, the presence/absence of radio waves transmitted by the other self-traveling vehicle B are confirmed, and when the radio waves are detected, a standby state for stopping traveling is attained. Also, when the radio waves from the other self-traveling vehicle B are not detected, the intersection area 2 is passed through while the radio waves are transmitted to the other self-traveling vehicle B. In this case, at the time of entering the intersection area 2, the time is differentiated at random, a reception operation and a transmission operation are alternately repeated for plural times and it is confirmed that the other self- traveling vehicle B is not in the intersection area 2. Thus, the probability that the transmission period and the reception period match between the two self-traveling vehicles is lowered to a value which can be practically considered as '0'.