A high-frequency signal amplifier includes an amplifier having an input terminal and an output terminal, and amplifying a high-frequency signal; a signal line connected between the output terminal of the amplifier and an antenna; coupled lines arranged in parallel and coupled to the signal line and having different line lengths or differently terminated ends; and phase shifters shifting phase of high-frequency signals applied via the signal line and the coupled lines, supplying the high-frequency signals to the input terminal of the amplifier, and having different amounts of phase change.