To help removing a tumor more safely without hindering procedures of surgery while a correct tumor region is identified.

The subject device is provided with a light source 2 which irradiates a chemically-modified fluorescent material collected at a diseased part OB of a patient PS with an exciting light having a prescribed wavelength, to intermittently excite the fluorescent material while the light is repeatedly turned on and off, an optical fiber 8 which guides the exciting light from the light source 2 near to the diseased part OB and receives the fluorescence radiated from the fluorescent material accumulated in the diseased part, a detecting unit 3 which detects the intensity of the inputted fluorescence through the optical fiber 8, an arithmetic unit 4 which estimates the concentration of the fluorescent material based on the fluorescence intensity detected by the detecting unit 3 corresponding to each lighting on or off state of the light source 2, and a display unit 5 which displays the estimated concentration of the fluorescent material calculated by the arithmetic unit 4.