A feed-forward amplifier of a type preventing unwanted waves from being outputted in an initial operation suitable to a use in a radio transmitter-receiver in a radio communication system, aimed to reduce a loss in the course from an output of a main amplifier to an output of the apparatus by implementing an output control during the initial operation in the front stage of the main amplifier without switches having been heretofore used, further reducing a power consumption of the apparatus. The feed-forward amplifier of this invention is provided with a control unit which controls a pilot signal variably attenuating unit so as to gradually decrease an attenuation quantity of a pilot signal with use of results of detection conducted by a power source start-up detecting means and a main signal detecting means as timing information after a start-up of a power source of a main amplifier, and controls a main signal variably attenuating unit so as to gradually decrease an attenuation quantity of a main signal after the pilot signal variable attenuating unit has decreased the attenuation quantity of the pilot signal.