A light source module includes at least one light source, first optical waveguide which causes light entering therein from a light inlet end face to emanate from a light outlet end face, and an inlet optical system which collects light emitted from the light source and couples it to the light inlet end face of the first optical waveguide. The light inlet end face of the first optical waveguide is larger than the light outlet end face thereof in cross-sectional area of the core.