The invention discloses a broadband amplifier. The broadband amplifier comprises a multi-stage current amplifying circuit, an outer feedback circuit, a self-biased circuit and an inner feedback circuit. The multi-stage current amplifying circuit comprises an emitting-electrode follow type primary amplification triode Q2 and a common-emitter type last-stage amplification triode Q3. The inner feedback circuit comprises an inner feedback resistor RFB1, a bias voltage resistor RB1 and a resistor R1. One end of the inner feedback resistor RFB1 is connected with one end of the bias voltage resistor RB1 to form a feed-in point. The outer feedback circuit comprises an outer feedback resistor RFB2, a capacitor C2, an outer feedback capacitor CFB and an outer feedback inductor LFB. The capacitor C2 is connected with the outer feedback capacitor CFB in parallel. The self-biased circuit comprises a bypass capacitor CB and a self-biased triode Q1. A collector electrode of the self-biased triode Q1 is connected with the feed-in point. By means of the broadband amplifier, the purpose that gain reduction is smaller than 0.2 dB within the whole frequency band range is achieved, and the application occasion of the broadband amplifier is broadened.