A method and apparatus for controlling a feedforward amplifier, wherein a superior distortion compensation characteristic is maintained over a wide frequency range, with the influence due to temperature variation and weathering minimized. A pilot signal generated by a pilot signal generator circuit is injected into the output of the main amplifier of a feedforward amplifier, and then the signal is sampled at the output of a first circuit and a second circuit, which is then low-range converted by a frequency converter and demodulated into I and Q components by a quadrature demodulator, and amplified and shaped into a pilot monitor signal; and a control circuit controls the vector adjusters within the distortion suppression circuit of the first and the second circuits using the I and Q signal components as the error signal so that as the amplitude level of pilot monitor signal is mininized the control value is maintained.