Abstract: An endoscope apparatus includes an optical system for forming an image of an object; a solid-state image sensor for receiving the image formed by the optical system; an illuminating device for irradiating the object with illuminating light; a light control device for changing the brightness of the illuminating light; a stop device whose aperture is variable, disposed in the optical system; a detecting device for detecting the brightness of the image of the object; and a control device for controlling the stop device and the light control device so that the intensity of a signal output from the solid-state image sensor is kept nearly constant in accordance with brightness information derived from the detecting device. In this way, the endoscope apparatus always maintains the optimum brightness of the image and ensures a practical pan-focus state in which a user's operation load is reduced.