A phase shifter includes a transformer connected between a first port and a second port and including a first coil and a second coil that is magnetically coupled to the first coil, the transformer including a parasitic inductance component; and an impedance adjustment circuit including a reactance element that suppresses a deviation in impedance due to the parasitic inductance component of the transformer. A coupling coefficient between the first coil and the second coil of the transformer and a value of the reactance element of the impedance adjustment circuit are determined such that a phase-shift amount changes in accordance with a frequency band.