A transmission front-end processor modulates the amplitude of a carrier wave with baseband data, and sets the power of the resultant modulated wave at a required value while controlling power leakage to adjoining channel to thereby output transmission data. The processor includes a first filter connected to an input terminal to which the baseband data are applied, for removing frequency components which would otherwise cause the power of the baseband data to leak to adjoining channels. The carrier wave and the baseband data passed through the first filter are applied to a power modulator. The power modulator controls the amplitude of the carrier wave with the baseband data, sets the power of the result of the control at the required value, and then outputs the power. A second filter removes higher order components from the carrier wave included in the output of the power modulator to thereby output the transmission data. The processor is capable of outputting high power without resorting to a linear amplifier.