A phase detector includes: a phase shift circuit to phase-shift a first positive-phase signal included in a first differential signal and a first negative-phase signal included in the first differential signal, and phase-shift a second positive-phase signal included in a second differential signal and a second negative-phase signal included in the second differential signal; a multiplication circuit to perform multiplication of two signals for all combinations of the first positive-phase signal and the first negative-phase signal with the phase-shifted second positive-phase signal and the phase-shifted second negative-phase signal, and perform multiplication of two signals for all combinations of the phase-shifted first positive-phase signal and the phase-shifted first negative-phase signal with the second positive-phase signal and the second negative-phase signal; and a phase difference calculating circuit to calculate a phase difference between the first differential signal and the second differential signal using multiplication signals of the multiplication circuit.