PURPOSE: To always obtain the correct decided result of the code of a demodulated output by using a reference voltage following the central value of an eye pattern.

CONSTITUTION: The voltage of a demodulated signal is stored and held in a capacitor 25 at specified timing prior to code deciding timing. Next, the code of the demodulated signal is decided at the code deciding timing, and the voltage level of the demodulated signal at the specified timing is estimated, and a switch 27 corresponding to said voltage level is operated, and the voltage of the difference between the voltage of the demodulated signal stored and held in the capacitor 25 at the specified timing and the reference voltage held in the capacitor 31 is held in the capacitor 28. The capacitors 28 are provided correspondingly to the kinds portion of the voltage levels in number, and the voltages they held are summed, and is made to pass through a low pass filter and makes the reference voltage. Thus, the voltage following the central value of the demodulated signal is obtained, and the decision which is never influenced by the central value variation due to DC cutoff and has few error can be realized.