Provided is a light source apparatus having a phosphor layer which is subjected to a light beam of a predefined wavelength emitted from a solid light source element as an excitation light beam and which generates fluorescent beam by being excited by the incident excitation light beam and emits the fluorescence beam to outside, and a metal layer which is joined to a predefined surface among outer surfaces of the phosphor layer except an incident surface of the excitation light beam and an outgoing surface of the fluorescence beam for converting excitons excited from a section of the phosphor layer close to the predefined surface into a light beam via surface plasmon polaritons. The light beam converted from the excitons via the surface plasmon polaritons is emitted out of the outgoing surface of the phosphor layer together with the fluorescence beam.