Observation is performed at a more appropriate sensitivity without causing deterioration of the image quality. Provided is a fluorescence observation apparatus (1) including an excitation light source (3) that emits excitation light to be radiated onto an imaging subject (A) a fluorescence-image acquisition portion (21) that is provided with an imaging device (18) that acquires fluorescence images (G2 and G3) by capturing fluorescence generated at the imaging subject (A) due to the irradiation with the excitation light emitted from the excitation light source (3) and a sensitivity adjusting portion (22) that adjusts an number of pixels for binning summing (B) and/or an exposure time for the imaging device (18) on the basis of luminance information of the fluorescence image (G2) acquired by the imaging device (18) of the fluorescence-image acquisition portion (21) so that an SN ratio of the fluorescence image (G2) becomes equal to or higher than a predetermined threshold.
