A transmitter using a channel aggregation in which available channels existing in various frequency bands are bound and transmitted and using an Orthogonal Frequency Division Multiplexing (OFDM), an Orthogonal Frequency Division Multiple Access (OFDMA), or a system similar to them as a modulation system. One or a plurality of transmission units are provided in parallel, and one or a plurality of transmission processing units are provided in parallel. The transmission processing unit has an inverse fast Fourier transforming circuit or a discrete inverse Fourier transforming circuit, a GI and overlap margin (OM) insertion circuit, and a time-domain windowing processing unit. The time-domain windowing processing unit multiplies a universal time-domain window function in accordance with a spectrum mask and transport electric power which are required in each channel, thereby suppressing out-of-band radiation electric power every channel. A kind and a window transition duration of the time-domain window function can be arbitrarily set every channel.