The probability of extracting a region containing a large amount of fluorescent material is increased in accordance with the kind of fluorescent reagent, variations among individuals, or variations in lesion sites. Provided is a fluorescence observation device (1) including an illuminating unit (3) that irradiates a subject (F) with excitation light and illumination light a fluorescence image capturing unit (18) that acquires a fluorescence image by capturing fluorescence generated at the subject (F) due to the irradiation with the excitation light a return-light image capturing unit (19) that acquires a return-light image by capturing return light returned from the subject (F) due to the irradiation with the illumination light an extracting unit (23) that determines and extracts a region having a gray level exceeding a gray-level threshold from the fluorescence image as a region-of-interest a display unit (7) that displays the region-of-interest extracted by the extracting unit (23) and the return-light image in association with each other a true/false input unit (8) that prompts an observer to enter true or false as to the determination of the region-of-interest displayed on the display (7) and a threshold updating unit (26) that updates the gray-level threshold so as to reflect the input result entered via the true/false input unit (8).
