To accomplish a backing function in a backing layer, and to reduce the diameter of the distal end hard part of an endoscope insertion tube.

The backing layer 22 constituting an ultrasonic vibrator array 24 in the distal end hard part of the endoscope insertion tube 2 is formed to be a substantially cylindrical shape. One or a plurality of notched parts are formed in a part of the inner peripheral surface. One member constituting an endoscope mechanism inside the backing layer 22 is partially protruded to the notched part. Then the outer diameter of a tunnel shape passage 25 is reduced. In the ultrasonic endoscope, the notched part is formed, so as to allow the total value of a distance for the progress of ultrasonic wave transmitted from ultrasonic vibrators 21 before being made incident to the notched part and a distance for the progress after being reflected against the notched part to be longer than a distance for the reciprocation of the ultrasonic wave transmitted from the ultrasonic vibrators 21 when regularly reflected against the backing layer 22 at a part other than the notched part.