A wavelength conversion device is provided. The wavelength conversion device includes a light-transmissive substrate that includes an incidence surface and an emission surface opposite the incidence surface. The light-transmissive substrate is configured to receive, by the incidence surface, excitation light and emit, from the emission surface, the excitation light. A phosphor layer is configured to emit fluorescent light when excited by the excitation light emitted from the emission surface. The phosphor layer includes a first phosphor layer and a second phosphor layer. The first phosphor layer includes first phosphor particles. The second phosphor layer includes second phosphor particles configured to emit fluorescent light including a peak wavelength longer than a peak wavelength of fluorescent light emitted by the first phosphor particles. The first phosphor layer includes a refractive index different from a refractive index of the second phosphor layer.