To provide a fluorescent diagnostic device capable of performing an additional treatment according to diagnostic results by allowing the device to quickly find a remained part which should have been cut, etc., in a tissue including an affected region.

Light of a HID lamp 3 is irradiated to a subject 8 mounted on a movable stage 7 through a band pass filter 4, lens 5, dichroic mirror 6 through which an excited light passes, the reflected light and the fluorescent light are introduced to a ICCD 19 by sequentially changing filters arranged on the light path of a rotary filter 13, the reflected and fluorescent images of the subject 8 are imaged, and they are converted into a video signal by a CCU 21 to inputted to an image processing circuit 22. With an image processing at the image processing circuit 22, the contours of the subject 8 and an affected part are detected, distance between the both contours is calculated, and the minimum value of the calculated distance is obtained and displayed together with a subject image on a color monitor 23 so that whether the affected part is cut completely or not can be determined.