A rigid tip end section which is connected to an angle section at the fore
distal end of an insertion instrument of an ultrasound endoscope is
housed in a casing which can be split into a main casing and a separable
head block to facilitate maintenance and service of internal component
parts of the rigid tip end section. An ultrasound transducer is
accommodated in a front side portion of the main casing, while endoscopic
observation means including an illumination means and an optical image
pickup means are fitted in an inclined wall rising obliquely upward on
the rear side of the ultrasound transducer. An outlet opening of a biopsy
channel outlet passage is located between the ultrasound transducer and
the endoscopic observation means. The main casing is adapted to
accommodate the ultrasound transducer and its wiring, while the separable
head block is adapted to accommodate at least part of component parts of
the endoscopic observation means. The main casing and the separable head
block are joined with each other through joint wall portions provided
along split lines at the opposite lateral sides and at the front side
thereof. A foremost one of angle rings of the angle section is detachably
fitted on base end portions of the main casing and separable head block
to retain these parts in a fixedly connected state.