To obtain a phase detector with a reduced phase rotation error by adjusting the decision area in accordance with the strength of a noise.

A first multiplexer part 30 is constituted of a multiplexers A30A and B30B. The multiplexer A30A outputs one of multiple left-shifted signals which are transmitted from a first shift part 20A to a subtracting part 140 by a selecting signal S decided by the strength of a noise signal. The multiplexer B30B outputs one of multiple right-shifted signals which are transmitted from the second shift part 20B to the subtracting part 140 by the selecting signal S decided by the strength of the noise signal. The selecting signal S is decided by a program to decide a largeness in shift. That is, a bit shift is reduced and the decision area is selected to be narrow when the influence of the noise is large. When the influence of the noise is weak, the bit shift is increased and the decision area is selected to be wide.