Variation in the illuminance of a light source device in the longitudinal direction is suppressed and the emitted light is efficiently emitted to an illuminated object. A light guide (3) propagates light emitted by a light source (1) and entering therein from an end in the long axis direction. A fluorescent material layer (5) surrounds the outer periphery of the light guide (3) except for an opening along the long axis direction, absorbs part of the light exiting from the periphery of the light guide (3), and emits fluorescence. A light reflecting pattern is provided on the outer periphery of the light guide (3) opposite to the fluorescent material layer (5). In the course of the light having entered therein from the end being propagated in the light guide (3), the fluorescent material layer (5) captures light reflected by the light reflecting pattern and exiting from the outer periphery of the light guide (3), reflects part of the light, and emits light of different wavelengths. Then, the light emitted by the fluorescent material layer (5) is transmitted into the light guide (3), and the light having entered therein from the end and the light emitted by the fluorescent material layer are emitted to the illuminated object from a portion of the light guide (3) that is exposed or protruding in the opening of the fluorescent material layer (5).