A wavelength converter which performs simultaneously wavelength conversion for a plurality of input light wavelengths that are unequally intervals, is provided. The nonlinear material of the wavelength converter has a modulation structure which has modulation of a nonlinear optical constant at a period Λ0 in a propagating direction of light, a phase being continuously changed each period Λ0 and a continuous phase modulation for a different period Λph being added to the modulation structure. The nonlinear material has a modulation structure obtained by changing a modulation curve for the phase modulation, wherein a phase mismatch Δβ is represented by Δβ=2π(n3/λ3−n2/λ2−n1/λ1), and at least three peaks at unequally intervals within a plurality of peaks for conversion efficiency represented by 2π/Λ0+2πi/Λf (i=m, m+1, . . . , n: where m and n are positive or negative integers) have highest conversion efficiency.