1. A fluorescence observation device comprising: an illumination light source that generates illumination light and excitation light to be radiated onto an examination subject; a return-light image generating unit that generates a return-light image by capturing return light coming from the examination subject due to the illumination light emitted from the illumination light source; a fluorescence image generating unit that generates a fluorescence image by capturing fluorescence generated at the examination subject due to the excitation light emitted from the illumination light source; a normalization computation unit that computes normalized fluorescence intensities, which are brightness values of individual pixels in the fluorescence image generated by the fluorescence image generating unit normalized by brightness values of corresponding pixels in the return light image; a standard-data storage unit that stores standard data that indicate a typical correspondence relationship between the normalized fluorescence intensities and states of the examination subject; and a state judging unit that judges the states of the examination subject that correspond to the individual normalized fluorescence intensities on the basis of a minimum value of the normalized fluorescence intensities computed by the normalization computation unit and the standard data stored in the standard-data storage unit.