Provided is an endoscope system (100) including a light source device (3) that outputs signal light that penetrates tissue within a living body a narrow medical instrument (1) that is inserted into a blood vessel and whose distal end has an emission window from which the signal light supplied from the light source device (3) is emitted an endoscope (5) that is inserted into the living body and has an imager (13), which obtains an optical image by acquiring an image of the living body, and a detector (13), which detects the signal light emitted from the emission window and an image processor (15) that generates a composite image by combining the optical image with a marker that indicates a position of the signal light.
