A phase shifter includes a first variable amplifier circuit configured to receive and amplify a first signal having a first phase; and a second variable amplifier circuit configured to receive and amplify a second signal having a second phase different from the first phase. The phase shifter is configured to generate an output signal having a desired phase by phase combination of an output of the first variable amplifier circuit and an output of the second variable amplifier circuit, and the first variable amplifier circuit and the second variable amplifier circuit each includes a plurality of amplifier circuit units. The amplifier circuit unit includes a first transistor with a grounded gate and a second transistor with a grounded source, and gains of the first variable amplifier circuit and the second variable amplifier circuit are specified according to the number of amplifier circuit units to be activated.