In an endoscope apparatus, an illuminating light is supplied from a light source unit to an end of an optical transmission system of an endoscope, and the optical transmission system has the other end allowing the illuminating light to be irradiated from an illuminating window located at a predetermined position of an inserting portion of the endoscope. The illuminating light has a luminous flux which is imaginarily divided into at least two regions including central and peripheral regions. An adjusting device is provided for adjusting a light quantity supplied to the one end of the optical transmission system through the central region of the luminous flux and a light quantity supplied to the one end of the optical transmission system through the peripheral region of the luminous flux, independently of each other.