A distal end part of an endoscope having a viewing window for introducing light from an object into an objective optical system for forming an observed image. An illuminating window is disposed in a side by a side relationship with the viewing window for illuminating a visual field of the objective optical system. A continuous transparent cover covers the surfaces of both the illuminating and viewing windows. A window glass is attached to the viewing window in such a manner that a virtual image of the outer edge portion of the window glass, which is produced by single reflection from the inner side of the outer surface of the transparent cover, lies outside the visual filed of the objective optical system.