To solve the problem that, when a waveform of an input signal is different from that of a feedback signal in a conventional decision feedback equalizer, unnecessary inter-code interference occurs and, when signals modulated by various modulation methods such as an RZ signal and an RZ-DPSK signal are input, equalization capability of the equalizer is degraded.

The decision feedback equalizer 18 executes appropriate waveform equalization without degrading performance by achieving waveform matching between an input signal and a feedback signal when waveforms having various modulation methods such as an RZ waveform and an RZ-DPSK waveform are input.