An amplifier circuit includes a first transistor, a second transistor, a first pathway and a second pathway. The first transistor amplifies an external signal that is input from outside the amplifier circuit. The second transistor amplifies a detection signal that detects a level of the external signal. The first pathway is connected between a collector of the first transistor and a base of the second transistor to supply the detection signal that is output from the collector of the first transistor to the base of the second transistor. The second pathway is connected between an emitter of the first transistor and the base of the second transistor to supply a bias voltage from the emitter of the first transistor to the base of the second transistor.