PROBLEM TO BE SOLVED: To provide a phototherapy apparatus allowing an operator to easily comprehend an already treated region and a non-treated region during an operation.SOLUTION: A phototherapy apparatus 1 performing phototherapy by use of a photosensitive substance administered to a living body includes: a light irradiation part 3 outputting first output light exciting the photosensitive substance to generate fluorescence and radiated to an observation region, and second output light exciting the photosensitive substance to generate singlet oxygen and radiated to a treatment region on the basis of the fluorescence emitted from the photosensitive substance an imaging part 4 imaging the observation region an imaged image generation part 51 generating imaged image data on the basis of an imaging signal from the imaging part 4 an already treated image generation part 55 generating already treated image data indicating a position irradiated with the second output light an image composition/display processing part 56 generating composite image data in which the already treated image data is superposed on the imaged image data and a display part 6 displaying the composite image data as a composite image.
