To accelerate a transmission rate by shortening the length of a guard interval in a radio communication system applying the system for transmitting an OFDM signal by providing directivity thereto.

A GI insertion part 105 inserts the guard interval to transmission data, delay addition parts 107-1 and 107-2 set delay time to the transmission data, and an arrival time calculation part 115 obtains arrival time from the transmission of the data from a communicating party to reception for each directivity from the reception data of each directivity. A delay time decision part 116 calculates the arrival time difference of the transmission data transmitted by two directivities and sets the calculated arrival time difference to the transmission data transmitted by the directivity of shorter arrival time as the delay time. A GI length decision part 117 sets the shortest arrival time among the obtained arrival time as the guard interval.