A light guide for a light source device includes a core layer which is formed from a transparent resin and has a refractive index n1 and cladding layers which are provided on both surfaces thereof and have a refractive index n2 which is lower than the refractive index n1 of the core layer. A light reflecting layer which scatters and reflects light is provided in the front surface of one cladding layer, the front surface of the other cladding layer is set as a light emitting face, and a recess is provided which reaches from at least one of either of the front surface of the one cladding layer or the front surface of the other cladding layer to the core layer passing through the cladding layer.