An object of the present invention is, in a communication path of which received 
signal quality is 
extremely poor, to prevent such a state of the communication failure. To a frame generator 13 in a 
transmitter 10, which transmits OFDM 
signal, a 
pilot & data arrangement format determiner 20, which determines 
pilot & data arrangement format of an OFDM 
signal based on the value of received 
signal quality at a 
receiver 30, a 
pilot symbol number determiner 19, which determines the number of pilot symbols based on the value of received 
signal quality, and a power amplification rate determiner 18, which determines power amplification rate based on the value of received 
signal quality, are newly provided. Thereby, it is possible to change the pilot & data arrangement format, the number of pilot symbols and the power amplification rate depending on the value of received signal quality to generate transmission signal frame of the OFDM signal. Owing to this, even in a channel of which received signal quality is poor, it is possible to satisfactorily reduce the 
transmission rate using adaptive modulation technique and maintain the channel 
estimation accuracy to a satisfactory level, and thus it is possible to prevent such a state of the communication failure.