Exciting light from a strobe light source is projected onto the fundus of the subject eye to excite a fluorescence substance in a subject eye fundus. Natural fluorescence exited in the fundus is received by a photodiode via a stop located at a position that is conjugate with the fundus. An XY stage is used to move the stop perpendicularly to the optical axis to change the measurement location. The output of the photodiode is used to calculate the intensity of the fluorescence from the measurement location. Since the measurement location can be changed with ease, it is possible to accurately and easily measure natural fluorescence from a desired part of the fundus.