Disclosed herein is a linear amplifier using a nonlinear amplifying stage which includes a first amplifier and a second amplifier connected in cascade, including: a bias voltage generator in which a first bias voltage is applied to a gate terminal of the first amplifier, and a second bias voltage higher than the first bias voltage is applied to a gate terminal of the second amplifier, wherein the first amplifier and the second amplifier have a nonlinear gain characteristic in a region of arbitrary output power, and as the output power increases in the region of arbitrary output power, a gain of the first amplifier increases, while a gain of the second amplifier decreases.