A wavelength conversion device enabling the stable output of high-power harmonic light is disclosed. The wavelength conversion device includes MgO:LiNbO3 (PPMgLN) having a periodic polarization reversed structure, and the +Z and −Z surfaces of the PPMgLN are covered with thin chrome (Cr) film. In the PPMgLN, the incident surface and output surface are disposed on the −X side and +X side, respectively, in the longitudinal direction. Because of this structure, even when a high-power laser fundamental wave is incident, the PPMgLN can avoid destruction and damage due to the electric field, thereby enabling the stable output of high-power harmonic.