Provided are a diagnosing device whereby a tumor site can be highly accurately identified, and an imaging method therefor. The tumor site diagnosing device, which irradiates porphyrins accumulated in a tumor site in the oral cavity with excitation light and detects luminescence generated by the porphyrins thus excited, comprises: a light irradiation section that irradiates the tumor site in the oral cavity with the excitation light； a light receiving section that receives the luminescence； and an image processing section that generates image data depending on the light intensity of the luminescence detected by the light receiving section.
