An object of the present invention is to provide a PDD diagnosis apparatus that even if there is a distance from an irradiation portion of an optical fiber to a diseased tissue, enables provision of a fluorescence detection sensitivity equivalent to that in a case where irradiation is provided in such a manner that the irradiation portion of the optical fiber is brought close to the diseased tissue. A diagnosis apparatus including: a light source unit that emits excitation light to a photosensitizing substance accumulated in a diseased tissue a detection unit that detects fluorescence produced from the photosensitizing substance and an excitation light irradiation/fluorescence detection optical fiber including an output/input end with a collimator connected thereto, in which the excitation light emitted from the light source unit is guided to the excitation light irradiation/fluorescence detection optical fiber, and the excitation light output from the output/input end is provided in such a manner that the excitation light is collimated by the collimator and excites the photosensitizing substance accumulated in the diseased tissue and the fluorescence produced by the photosensitizing substance excited by the excitation light is input from the output/input end via the collimator, and the input fluorescence is guided to the excitation light irradiation/fluorescence detection optical fiber and the fluorescence produced from the photosensitizing substance is detected in the detection unit is used.
