An endoscope system includes a light source unit, an image sensor, an image signal obtaining section, a vessel position signal generator, a vessel width signal generator, and a vessel image signal generator. The light source unit generates illumination light. The image sensor captures an image of an object of interest irradiated with the illumination light. The image signal obtaining section obtains an image signal, which represents the object, from the image sensor. The vessel position signal generator generates a vessel position signal, which represents the position of a blood vessel of the object, from the image signal. The vessel width signal generator generates a vessel width signal, which represents the width of the blood vessel, from the image signal. The vessel image signal generator generates a vessel image signal, which represents the blood vessel, from the vessel position signal and the vessel width signal.