Disclosed is a duobinary optical transmission apparatus. The duobinary optical transmission apparatus uses the crossed phase characteristics of a duobinary signal without using a feedback-type precoder and an electric LPF, and is thereby not affected by Pseudo-Random Bit Sequence (PRBS), and is very resistant to wavelength division characteristics. In addition to a drive amplifier, a Mach-Zehnder-interferometer-type optical intensity modulator (MZ MOD), and a laser source for generating a carrier wave, the duobinary optical transmission apparatus further includes a toggle flip-flop (T.FF) and an AND gate to separate a group of `1` from input data signal in such a way that the input data signal is modulated to make each signal have a different phase.