An optical signal generating unit (110) applies a modulation based on a drive signal to a carrier, thereby generating an optical signal to be transmitted. A filtering unit (120) filters the drive signal. The filtering unit (120) may perform a time domain equalization or a frequency domain equalization. More particularly, the filtering unit (120) filters the drive signal, thereby keeping an integration value, which is obtained by integrating, in the frequency direction, the power spectrum density of the optical signal to be transmitted, equal to or greater than a first reference value, while making the peak value of the power spectrum density of the optical signal to be transmitted equal to or less than a second reference value.
展开▼
