Affords a wavelength converter manufacturing method and a wavelength converter whereby the transmissivity can be improved. A method of manufacturing a wavelength converter (10a) is provided with the following steps. At first, crystal is grown. Then a first crystal (11) and a second crystal (12) are formed by sectioning the crystal into two or more in such a way that the domains are the reverse of each other. The first and second crystals (11) and (12) are then interlocked in such a way that a domain inversion structure in which the polar directions of the first and second crystals (11) and (12) periodically reverse along an optical waveguide (13) is formed, and the domain inversion structure satisfies quasi-phase-matching conditions for an incoming beam (101).