PURPOSE: To prevent the interference between the radiowaves from radio transmitters and to make it possible to receive data accurately by controlling the outputs of a plurality of radio transmitters which are provided in close proximity, and transmitting the signals at the different times.

CONSTITUTION: Beacon transmitters 1a and 1b transmit signals to a receiver 3 which is provided in a vehicle 2 such as a bus. The transmitters 1a and 1b are provided in close proximity. In this constitution, the vehicle 2 on a read A is guided to either of a road B or a road C at the junction of the three rods. At this time, two signals S1 and S2 having the time difference are transmitted from the transmitters 1a and 1b to the receiver 3 which is mounted on the vehicle 2. Even if the transmitters 1a and 1b are arranged in close proximity, the radiowaves S1 and S2 from both transmitters are not interfered. Therefore, even though the vehicle is located within the interfering zone D, the receiver 3 can receive the detailed data accurately.