1. A sentinel lymph node detection method, comprising focusing a fluorescent image composed of fluorescent light having a wavelength band within the near-infrared wavelength band emitted from a near-infrared fluorescent colorant, which emits fluorescent light having a wavelength band within the near-infrared wavelength band, that has been injected into the area of tissue under examination in the vicinity of a diseased portion, which includes the sentinel lymph node, upon irradiation thereof by stimulating light, and converting said focused fluorescent image composed of fluorescent light having a wavelength band within the near-infrared wavelength band to a visible image.