A control unit generates packet signals to be transmitted. The control unit uses either a first packet format, where a second known signal defined by a second radio communication system different from a first radio communication system is assigned anterior to a first known signal defined by the first radio communication system, or a second packet format, where the first known signal is assigned in an anterior part. Subcarriers to be used in the first known signal contain subcarriers to be used in the second known signal, and the first known signal and the second known signal are defined by different values.