PURPOSE: To perform effective optical communication, by providing an optical filter to which a signal to be transmitted signal only passes through for an optical fiber output terminal and detecting light passing through an optical filter.

CONSTITUTION: A laser light source 1 generates a pumping light ωp of continuous oscillation and a laser light source 2 generates a laser light ω1 in the wavelength of Stokes light including the term of high order generated with simulated Raman oscillation from the pumping light in an optical fiber. A synthesizer 4 synthesizes both signals and transmits the output in an optical fiber 5. An optical filter 6 is provided at the output terminal of the optical fiber 5, and the light in wavelength ω1 only passing through this filter 6 is detected at a detector 7, and thus, the transmission/reception of optical signals can be performed.