A parity error detecting circuit includes a first operation unit, a second operation unit, and a shift register. The first operation unit receives a serial data signal and a first signal, performs a logic operation on the two received signals, and outputs the result of the logic operation as the first signal in response to a first clock signal. The shift register shifts the first signal in response to the first clock signal and outputs a second signal. The second operation unit receives the first signal and the second signal, performs a logic operation on the two received signals, and outputs the result of the logic operation in response to a second clock signal.