A fluorescence detecting apparatus includes an excitation light applying section that applies excitation light to a protective film containing an absorbing agent. A photomultiplier tube detects fluorescence emitted from the absorbing agent due to absorption of the excitation light. A fluorescence passing filter removes light having wavelengths other than the wavelength of the fluorescence emitted from the absorbing agent, and a reflecting mirror having a reflecting surface reflects the fluorescence emitted from the protective film toward the photomultiplier tube. This reflecting surface is formed by a part of a curved surface forming a spheroid having first and second foci. The first focus is positioned at a target area of the protective film where the excitation light is applied, and the second focus is positioned at a light detecting element included in the photomultiplier tube.