In an electronic endoscope system (303), the intensity of therapeutic light projected from a therapeutic light unit (62) into a subject body may be lowered by a stop mechanism (72) to avoid halation. With the low intensity therapeutic light and ordinary white light from an illumination light unit (61), a CCD (21) captures an image from an interior of the subject body. From the captured image, an irradiance estimator (303) extracts data about the position and power distribution of irradiation by the therapeutic light. A display control circuit (44) controls a monitor (22) to display the extracted data in combination with the captured image, allowing the operator to adjust the projected position and direction of the therapeutic light to be efficient for photodynamic treatment.
