A method of detecting an accessory cancer lesion, comprising an administration step wherein indocyanine green is administered to a living body, an irradiation step wherein a target organ suspected of having cancer is surgically exposed and irradiated with excitation light of indocyanine green, an imaging step wherein a near-infrared fluorescence intensity distribution image from the excited indocyanine green in the target organ is obtained, and an identification step wherein an area having the near-infrared fluorescence in the intensity distribution image, excluding the area detected in preoperative examination or intraoperative macroscopic observation, is identified as an accessory cancer lesion.