In photodynamic diagnosis and photodynamic therapy, the oscillating wavelength of laser light from a light source is fitted to a plurality of different kinds of photosensitizers and exciting conditions thereof. Moreover, diagnosis and treatment are achieved using concurrent diagnosis during treatment is realized as well. A semiconductor laser generates laser light having an oscillating wavelength which is variable and a full width at half maximum which is narrow. A light transmission line guides an irradiated laser light to the vicinity of a focus, an image transmission line observes the focus and the periphery thereof, a fluorescence light extracting device extracts only the fluorescence light emitted from a photosensitizer excited by the irradiated laser light, an image-pick-up/analyzing device picks up and analyzes an image of the extracted fluorescence light and an image display device displays the analyzing result.