Regions where metastatic cancer cells can exist are detected with high accuracy in a sentinel lymph node. Quantum dots are injected into the vicinity of a cancer in a living body, thereby identifying the location of the sentinel lymph node by means of fluorescence. Subsequently, the sentinel lymph node is extracted. With respect to the sentinel lymph node extracted with quantum dots injected, structural analysis is conducted by means of precision fluorescence measurement which uses a confocal fluorescence microscope for monomolecular observation. Specifically, the fluorescence intensity is measured with respect to each of multiple areas in the sentinel lymph nodes, and out of the multiple areas measured, one or more areas are detected as afferent lymph vessel inflow regions in descending order of fluorescence intensity.