PURPOSE: To revise the configuration of the amplifier and to attain simple broad band without changing the size of a separator and coupler itself with respect to the balanced type amplifier amplifying a signal at a broader band than the frequency band of the coupler.

CONSTITUTION: The gain of amplifiers 2-1, 2-2 at a frequency at the out-band of a 1/4 wavelength separator 3 and a 1/4 wavelength coupler 4 is selected to be higher than the gain in the band in the balanced type amplifier in which an input signal from an input terminal 1 is separated by the 1/4 wavelength type separator 3, each output of each separator 3 is connected respectively to amplifiers 2-1, 2-2, each output is amplified by the amplifiers 2-1, 2-2, coupled by the 1/4 wavelength type coupler 4 to obtain an output.