An ultrasound endoscope includes: an insertion portion； an ultrasound functional unit including an ultrasound transducer； an endoscope functional unit that at least includes an imaging optical system； and a balloon locking portion configured to connect the ultrasound functional unit and the endoscope functional unit, the balloon locking portion having a groove shape that can lock a balloon. A first plane passes, in a direction of a longitudinal axis of the insertion portion, through a first end portion of the ultrasound transducer near the endoscope functional unit, the first plane being perpendicular to the longitudinal axis of the insertion portion, and the first plane is positioned closer to a proximal end than a second plane passing through a second end portion of the balloon locking portion near the ultrasound functional unit, the second plane being perpendicular to the longitudinal axis of the insertion portion.
