A wavelength conversion device includes a substrate, a reflection layer, a wavelength conversion layer, and a first optical layer. The wavelength conversion device has a central axis. The reflection layer is disposed on an upper surface of the substrate. The central axis is perpendicular to the upper surface. The wavelength conversion layer is disposed on the reflection layer and around the central axis, has a complete or partial annular shape, and includes a first region and two second regions. The first region is located between the second regions. The first optical layer is disposed on a surface of the wavelength conversion layer and corresponds to the first region. In an axial direction, an orthographic projection of the first optical layer on the upper surface is not overlapped with an orthographic projection of the second regions on the upper surface. The first optical layer includes first diffusing particles.