In a transmission device 101, a modulation portion 102 carries out modulation of encoded data based on an adaptive modulation command based on feedback information sent from the receiving side, a frequency symbol diffusion block 105 multiplies the plurality of signals outputted by a serial-parallel conversion portion 104 by an orthogonal diffusion code and combines them, a pseudo random-number multiplication portion 106 multiplies each of them by a pseudo random number, an inverse Fourier transform portion 107 conducts inverse Fourier transform, a parallel-serial conversion portion 108 conducts parallel-serial conversion, a guard interval addition portion 109 adds a guard interval and a transmission portion 110 transmits a signal so that only one feedback information and modulation level information is required for each frequency symbol diffusion block 105 and transmission rate can be improved.