A wavelength conversion device is provided that includes: light-transmissive substrate that includes an incidence surface and an emission surface opposite the incidence surface, and emits, from the emission surface, laser light that enters the incidence surface; a phosphor layer that emits fluorescent light when excited by the laser light emitted from the emission surface; and a light diffuser layer between the emission surface and the phosphor layer. The light diffuser layer is, when viewed in a direction perpendicular to the emission surface, disposed only in a portion of a region in which the phosphor layer is disposed.