Provided is a fluorescence observation device including: a processor configured to: extract, as a candidate region of interest, a region in a corrected fluorescence image that has a gradation value larger than a gradation-value threshold, the gradation-value threshold being set based on an average of gradiation values, a standard deviation, a first coefficient, and a second coefficient; receive a result, inputted by an observer, as to whether a candidate region of interest displayed on a display is a result of right indicating a determination by the observer that the candidate region of interest is a region of interest or a result of wrong indicating a determination by the observer that the candidate region of interest is not a region of interest; and set at least one of the first coefficient and the second coefficient so as to reflect the result inputted by the observer.