For a first transistor, a source thereof is coupled to an input terminal and a drain thereof is coupled to an output terminal. A first variable impedance circuit is arranged between a gate of the first transistor and ground, and the impedance thereof is changed according to a first control signal. A second variable impedance circuit is arranged between the gate and the source of the first transistor, and the impedance thereof is changed according to a second control signal. Furthermore, an impedance circuit is arranged between the gate of the first transistor and a power supply. The ratio of the impedances of the first and second variable impedance circuits can be set to an arbitrary value according to the first and second control signals in order to change the gain of the low noise amplifier. As the result, the generation of unwanted thermal noise can be prevented.