Abstract: A wavelength converter includes: a first multiplexer that combines input signal light with wavelength-conversion excitation light; a second multiplexer that combines the signal light with Raman excitation light; a first nonlinear optical medium that generates wavelength-converted light of the signal light, based on a nonlinear optical effect; and a second nonlinear optical medium that amplifies wavelength-converted light of the signal light output from the first nonlinear optical medium. A wavelength of the Raman excitation light being a wavelength within an amplification band that allows Raman amplification of wavelength-converted light.