An endoscopic insertion tube is composed of an elongated flexible tube section, an articular section and a rigid tip end section in series from a proximal end which is connected to a manipulating head grip. At least an illumination window and an endoscopic observation window are provided on a distal end face of the rigid tip end section which is tapered off gradually from its proximal end on the side of the articular section, i.e., the thickest portion of the insertion tube. A transitional section which is provided between the articular section and the flexible tube section is tapered off in an inverse direction, gradually from the articular section toward the elongated flexible tube section.
