A transmitter in which: channel aggregation is adopted for bundling and transferring usable channels present in a variety of frequency bands; and OFDM, OFDMA, or a similar method is adopted as a modulation scheme, wherein one or more transmission units are provided in parallel to the latter stage of a subcarrier mapping circuit, the transmission units being provided in corresponding fashion to one or more frequency bands, and one or more transmission processing units are provided in parallel to each of the transmission units, the transmission processing units being provided in corresponding fashion to one or a plurality of channels. The transmission processing units each have a high-speed inverse Fourier transform circuit or a discrete inverse Fourier transform circuit, a GI and overlap margin (OM) adding circuit, and a time-axis windowing processing unit. The time-axis windowing processing unit multiplies a desired time-axis window function according to the spectrum mask or transmission power required by eac
