A method is provided to label invisible fluorescence by a visible light. A surgeon gets rid of screen for direct observation without repeated location confirmations between surgical site and onscreen mark. Fluid movement of a fluorescent dye can be observed in a real-time mode. Through projecting a visible-light spot at a fluorescent area at real time, the surgeon observes the fluorescent area the visible-light spot projecting to. Hence, the problem that fluorescence imaging technology must rely on screen to see the location of the fluorescent area is solved. When a patient moves or fluorescent areas changes, an image sensor automatically adjusts an area labeled by a visible-light spot through changing a photographing area with a focus automatically set. In addition, the method adjusts a projecting angle of the visible-light spot with an initial mirror and a final mirror only. Adjustment of lens group is not required the saving money.
