In a gain switching LNA including a first transistor, a first transistor group (for example, second to ninth transistors) and a second transistor group (for example, tenth to seventeenth transistors), a first resistor connected between an emitter of the tenth transistor and a collector of the first transistor and a second resistor connected to emitters of eleventh to seventeenth transistors and the collector of the first transistor and having a resistance one seventh as high as that of the first resistor are provided. In a high-gain mode, since isolation of the tenth to seventeenth transistors which are turned OFF and the first and second to ninth transistors is secured by the first resistor and the second resistor, there is no deterioration in the noise factor.