To enable wavelength conversion near to signal light by outputting only the wavelength conversion light without using an optical filter with a wavelength converter utilizing the oscillation suppression phenomenon of a semiconductor laser.

An optical amplifier region is inserted into two arm waveguides 13a, 13b of a symmetrical Mach-Zehnder interferometer. The wavelength converter has a light reflection means for reflecting the light of a wavelength Ac to input/output ports which are the cross ports of the symmetrical Mach- Zehnder interferometer. A laser resonator is formed by this light reflection means and the optical amplifier region to induce the laser oscillation of the wavelength λc. At this time, intensity modulation signal light of a wavelength λs is inputted from the port to which the light reflection means is not connected. The wavelength conversion light formed by the complementary modulation of the laser oscillation light of the wavelength λc by the intensity modulation signal light of the wavelength λs is separated from the intensity modulation signal light and is outputted from the different port.