To detect a transmission frame with an independent correlation processing by arranging an OFDM symbol for transmission frame detection, which is generated by orthogonal frequency division/multiplex modulation through the use of plural frequency sub-carriers, in the transmission frame and transmitting it.

An OFDM signal which is converted into an analog signal by D/A converters 11 and 12, is band-restricted by LPF 13 and 14 and is inputted to an orthogonal modulation circuit 15. In the orthogonal modulation circuit 15, the outputs of the LPF 13 and 14 are converted into intermediate frequencies with a sine wave from an oscillator 18 and a cosine wave from a π/2 phase shifter 19 in frequency mixers 16 and 17. The outputs of the frequency mixers 16 and 17, which are converted into the intermediate frequencies, are synthesized in a synthesizer 20 and a BPF 21 restrict a band. The output of the BPF 21 is amplified by an amplifier 22 and a synthesizer 23 and a frequency mixer 24 convert the frequency into a radio frequency. The output of the frequency mixer 24 is band-restricted in a BPF 25 and it is outputted as an RF signal.