A probe of an endoscope comprises a light guide fiber bundle and an image guide fiber bundle. The light guide fiber bundle supplies illumination light to the distal end of the probe, to illuminate the observed object. The illumination light is reflected by the observed object, and enters the end surface of the image guide fiber bundle. A ratio of an illumination sectional area of the light guide fiber bundle to a light receiving sectional area of the image guide fiber bundle is made equal.