An illumination device includes a wavelength conversion material layer with a first surface, which includes a wavelength conversion material and a scattering material; a light guide device located adjacent the wavelength conversion material layer on a side facing its first surface for directing an excitation light onto the first surface of the wavelength conversion material layer, and for directing a mixed light emitted from the first surface, which includes converted light and remaining excitation light not absorbed by the wavelength conversion material layer, into a light exit port. In this illumination device, the light guide device can collect the excitation light reflected by the wavelength conversion material layer effectively, which insures that adding scattering materials into the wavelength conversion material layer doesn't have a significant impact on the luminous efficiency of the illumination device, and resolves the conflict between color uniformity and luminous efficiency of the device.