A technique for reducing the looseness of a wire and reducing the positional error of an ultrasonic transducer is disclosed. According to the technique, inside a tip portion 3 of an insertion portion 2, middle pulleys 11a, 11b are placed between pulleys 6, 7. The middle pulley 11a is attached to a slider portion 14, and the slider portion (and the middle pulley 11a) is supported slidably in the direction orthogonal to the rotation direction of the pulley 6 along a slider guide portion 15 formed at the tip portion, and the position of a sliding direction is supported so as to be able to be fixed at the tip portion by a screw 13.
