An ultrasound endoscope according to the present invention includes an insertion portion to be inserted into a subject, and includes: an ultrasound functional unit provided at a distal end of the insertion portion, the ultrasound functional unit including an ultrasound transducer configured to transmit and receive an ultrasound wave on a surface including a longitudinal axis of the insertion portion, the surface being parallel to the longitudinal axis； and an endoscope functional unit connected to the ultrasound functional unit, the endoscope functional unit at least including: a balloon locking portion having a groove shape that can lock a balloon； and an imaging optical system, wherein a first plane passes, in a direction of the longitudinal axis of the insertion portion, through an 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 an end portion of the endoscope functional unit near the ultrasound functional unit, the end portion of the endoscope functional unit being a boundary between the ultrasound functional unit and the endoscope functional unit.
