Provided is a wavelength converter that makes it possible to improve the S/N ratio of output signal light. In the wavelength converter, optical pump light ₃ output from an optical pump source passes through a first reflector and travels through an optical fiber. Light having wavelengths that differ from the aforementioned wavelength is generated by a nonlinear optical phenomenon at the optical fiber. Of the light, generated light ₄ having a resonant wavelength of a resonator is optically amplified and oscillated. An input signal ₁ also passes through the first reflector and travels through the optical fiber. At the optical fiber, an output signal light ₂ having a different wavelength is generated by a nonlinear optical phenomenon between the generated light ₄ and the input signal light ₁. The output signal light ₂ passes through a second reflector and is output from a resonator.