To provide a multiband high-frequency amplifier wherein by using a single function part, gain control over a plurality of variable amplifiers is attained.

The multiband high-frequency amplifier comprises the plurality of variable amplifiers which amplify modulated signals of different frequency bands with a gain, corresponding to a negative feedback control input; a pair of microstrips MSL which have extension of a 1/4 wavelength of a signal, in the lowest frequency band among the frequency bands that those variable amplifiers match and are disposed closely, at a distance where they can be coupled to each other with an electromagnetic field; a coupling length varying means for varying the coupling length of the MSLs to a 1/4 wavelength of a signal in a frequency band designated with a switching control input; a selecting means for selectively inputting the output of a variable amplifier, corresponding to the frequency band designated with the switching control input to a main line as one of the MSLs; a detecting means for detecting a coupling output extracted by a subordinate line as the other of the MSLs; and an error detecting means for inputting the difference between a detection output and a predetermined reference value as the negative feedback control input, to the variable amplifier.