Two antennas are provided in a base station, one antenna AT1 is arranged at the root of a right handle grip [1R] and the other antenna AT2 is arranged at the root of a left handle grip [1L]. Alternatively, one antenna AT1 is arranged at the root of a front right turn signal [2R] and the other antenna AT2 is arranged at the root of a front left turn signal [2L] Alternatively, one antenna AT1 is arranged at the root of a rear right turn signal [3R] and the other antenna AT2 is arranged at the root of a rear left turn signal [3L]. Alternatively, one antenna AT1 is arranged at the front of a vehicle and the other antenna AT2 is arranged at the rear thereof.