A feedforward amplifier includes a main amplifier for amplifying an input signal, a control circuit for generating a predetermined pilot signal based on the output of a local oscillator and a frequency divider included in the control circuit, and a coupler for combining the input signal or the amplified signal with the pilot signal to generate a combined signal. A first coupler and a second coupler are provided for extracting any distortion component from the combined signal. A vector adjuster, an error amplifier, and a third coupler are provided for removing the extracted distortion component from the combined signal to generate an output signal. An orthogonal detector is provided for using any one of the pilot signal, or the output of the local oscillator, the frequency divider, and the combination of the vector adjuster, error amplifier, and the third coupler to make an adjustment for removing the distortion component.