To reduce the influence of Doppler shift, with the sub-carrier interval being widened in a high-frequency band, transmission timings of frames for every frequency band are matched each other. By matching the frame transmission timings, at the receiving side, once the modulation timing in one frequency band is detected, the modulation timing at another frequency band can be obtained. Therefore, demodulation can be simplified. To match the frame transmission timings, the CP length is adjusted, for example.