An ultrasound endoscope 1 including, at a distal end of an insertion portion 2 to be inserted to a body cavity, a distal rigid portion 2a arranged forward of a flexible tube portion 2c, an ultrasound transducer portion 10 for scanning a plane which is parallel to forward side of a longitudinal center axis L1 of the distal rigid portion 2a, and a treatment instrument insertion channel port 27 opening in a distal-side end face of the distal rigid portion 2a, with a longitudinal center axis L4 being parallel to the longitudinal center axis L1 of the distal rigid portion.
