A lymph node detecting apparatus comprising: an excitation light source unit having a plurality of excitation light sources (2, 2a), each of the light sources illuminating excitation light onto a living body observation portion that includes a lymph node near a tumor into which a fluorescent dye that emits fluorescence of a predetermined wavelength has been injected in advance; an optical filter, transmitting a fluorescence image generated from the living body observation portion; an image pickup means, picking up the fluorescence image transmitted through the optical filter; an adjusting means, adjusting at least one of a luminance and a contrast of an observation image output from the image pickup means; an image displaying means, displaying the observation image, adjusted by the adjusting means, as an image for detecting the lymph node; a supporting plate, on one surface of which the plurality of excitation light sources are installed, the supporting plate having an opening at a central position that includes a central axis (Ax) of the excitation light source unit, the central axis (Ax) is an optical axis of the detecting apparatus, and the plurality of excitation light sources are arrayed two-dimensionally so as to surround the opening, and the optical filter is configured to transmit the fluorescence image and transmit, at a predetermined light intensity, a reflection image of the excitation light from the living body observation portion illuminated by the excitation light, wherein the reflection image is transmitted at a light intensity no more than the fluorescence intensity of the fluorescence image. an excitation light source unit having a plurality of excitation light sources (2, 2a), each of the light sources illuminating excitation light onto a living body observation portion that includes a lymph node near a tumor into which a fluorescent dye that emits fluorescence of a predetermined wavelength has been injected in advance; an optical filter, transmitting a fluorescence image generated from the living body observation portion; an image pickup means, picking up the fluorescence image transmitted through the optical filter; an adjusting means, adjusting at least one of a luminance and a contrast of an observation image output from the image pickup means; an image displaying means, displaying the observation image, adjusted by the adjusting means, as an image for detecting the lymph node; a supporting plate, on one surface of which the plurality of excitation light sources are installed, the supporting plate having an opening at a central position that includes a central axis (Ax) of the excitation light source unit, the central axis (Ax) is an optical axis of the detecting apparatus, and the plurality of excitation light sources are arrayed two-dimensionally so as to surround the opening, and the optical filter is configured to transmit the fluorescence image and transmit, at a predetermined light intensity, a reflection image of the excitation light from the living body observation portion illuminated by the excitation light, wherein the reflection image is transmitted at a light intensity no more than the fluorescence intensity of the fluorescence image.