An ultrasound endoscope, includes: an insertion portion configured to be inserted into a subject, acquire an optical subject image, and transmit and receive ultrasound; an ultrasound transducer configured to emit the ultrasound in a direction perpendicular to a longitudinal direction of the insertion portion, and perform scanning in a circumferential direction of an axis parallel to the longitudinal direction; a forward field optical portion that is provided at a distal end of the insertion portion in the longitudinal direction, the distal end being where observation light coming from a forward field enters; and a side field optical portion that is provided at a distal end side of the insertion portion in the longitudinal direction and is where observation light from a side field including a part of a scan plane of the ultrasound transducer enters, the side field being a field in a direction perpendicular to the longitudinal direction.