The present invention has as its object the provision of a fluorescence light source apparatus which has high reliability without a drop in reflectance over a long period of time. The fluorescence light source apparatus of the present invention includes a fluorescent plate that emits fluorescence under excitation light and has a front surface serving as an excitation light incident surface, a reflection layer that is disposed on a back surface side of the fluorescent plate, and a heat dissipation substrate, wherein a sealing layer covering a back surface and a peripheral side surface of the reflection layer is provided in close contact with a peripheral area of the back surface of the fluorescent plate via an adhesion layer, and a diffusion prevention layer formed by nickel plating is provided on the heat dissipation substrate via a bonding member layer.