A pre-equalized optical transmitter includes, a laser source; a duo-binary pre-coder circuit; a pre-equalization circuit for applying an inverse function of chromatic dispersion; at least two D/A converters; and an optical field modulator comprising at least two input terminals for an electric signal. The pre-equalized optical transmitter: converts, by the duo-binary pre-coder circuit, a digital information signal of a predetermined symbol time to be transmitted into a digital complex signal including one sampling point per symbol; equalizes, by the pre-equalization circuit, degradation in transmission of the digital complex signal; converts, by the D/A converters, the equalized digital complex signal into an analog signal; suppresses an analog signal leaking outside a Nyquist bandwidth by at least 23 dB; modulates, by the optical field modulator, light output from the laser source with the analog signal to generate a modulated optical field signal; and transmits the modulated optical field signal.