The present invention provides a fluorescence observation device with which a region comprising a large number of fluorescent substances is specified without complex calculations being performed, even when the intensity of fluorescence changes due to distance or angle. The fluorescence observation device (1) is provided comprising: an illumination unit (3) which illuminates a subject (A) with excitation light and illumination light a fluorescent imaging unit (18) which acquires a fluorescence image (S2) by capturing an image of fluorescence generated in the subject (A) as a result of illumination with the excitation light from the illumination unit (3) a return-light imaging unit (17) which acquires a return-light image (S1) by capturing an image of the return-light that returns from the subject (A) due to illumination with the illumination light from the illumination unit (3) a region extraction unit (24) which extracts a high-brightness region where the fluorescence image (S2) acquired by the fluorescent imaging unit (18) has a gradation value of at least a set threshold value (S4) and a threshold setting unit (22) which increases the threshold value (S4) in response to increases in the gradation value of the return-light image (S1) acquired by the return-light imaging unit (17).La présente invention porte sur un dispositif dobservation de fluorescence, grâce auquel dispositif une région comprenant un grand nombre de substances fluorescentes est spécifiée sans que des calculs complexes ne soient réalisés, même lorsque lintensité de fluorescence change du fait de la distance ou de langle. Le dispositif dobservation de fluorescence (1) comprend : une unité déclairage (3) qui éclaire un sujet (A) avec une lumière dexcitation et une lumière déclairage une unité de réalisation dimage de fluorescence (18) qui acquiert une image de fluorescence (S2) par capture dune image de fluorescence générée dans le sujet (A) en résultat dun éclairage avec la lumière dexcitation pro
