To provide a device for converting an optical wavelength, which has only a few branching points and with which modulated input signal light is efficiently utilized.

The device A1 for converting the optical wavelength is equipped with an MZI 4. The MZI 4 is equipped with a pair of optical paths for interference consisting of optical paths 5, 6. A first SOA 1 is interposed in series with the optical path 5 and a second SOA 2 is interposed in series with the optical path 6. Also an optical path 7 to input modulation input signal light to the first SOA 1, an optical path 8 to input signal light to be subjected to wavelength conversion to the MZI 4 and an optical path 9 to output signal light with a converted wavelength from the MZI 4 are connected to the MZI 4. The MZI 4 is equipped with an optical path 10 to mutually connect the optical paths 5, 6. The first SOA 1 and the second SOA 2 are connected in series toward the modulation input signal light via the optical path 10.