Provided is a fluorescence observation device comprising an illuminating section that emits excitation light and illumination light onto a subject a fluorescence-image capturing section that acquires a fluorescence image by image-capturing fluorescence generated in the subject by irradiation with the excitation light from the illuminating section a return-light-image capturing section that acquires a return-light image by image-capturing return light that returns from the subject by irradiation with the illumination light from the illuminating section a region extracting section that extracts a high-luminance region in which the fluorescence image acquired by the fluorescence-image capturing section has a gradation level higher than or equal to a set threshold value and a threshold setting section that sets the threshold value higher as the gradation level of the return-light image acquired by the return-light-image capturing section increases.
