A phosphor device of an illumination system emitting a first waveband light and having an optical path includes a first section and a first phosphor agent. The first phosphor agent is coated on the first section. The first waveband light is received and converted into a second waveband light by the first phosphor agent. The second waveband light is directed to the optical path. The range of the spectrum of the second waveband light includes at least a first color light and a second color light, so that the first color light or the second color light is separated from the second waveband light along the optical path. Therefore, the diversity of the design of the phosphor device is enhanced, the manufacturing cost and the size of product are reduced, and the color purity is enhanced.