a signal transmitting apparatus using orthogonal frequency division multiplexing includes an inverse fast fourier transform circuit for converting a digital information signal into a first multi - value qam modulation signal . a guard interval setting circuit is operative for periodically generating a guard interval signal equal to a time segment of the first multi - value qam modulation signal , and inserting the guard interval signal into the first multi - value qam modulation signal to convert the first multi - value qam modulation signal into a second multi - value qam modulation signal . a clock signal generating circuit is operative for generating a first clock signal which drives the inverse fast fourier transform circuit , and generating a second dock signal which drives the guard interval setting circuit . the inverse fast fourier transform circuit includes a device for generating a pilot signal which corresponds to a given - order carrier , and adding the pilot signal to the first multi - value qam modulation signal . the pilot signal has a predetermined frequency and an angle modulation component which remains constant over a plurality of symbol periods . the pilot signal corresponding to a given integer times its wavelength or a given odd number times its half wavelength is present in a guard interval occupied by the guard interval signal in the second multi - value qam modulation signal . the pilot signal is continuously present over the guard interval and another interval .