The invention has an object of providing an ultrasound observation apparatus that is easily inserted and for this object the invention includes: an ultrasound transducer 21 that includes an ultrasound transmitting/receiving face 21a that transmits/receives ultrasound； a holding part 22, 23 that fixedly holds the ultrasound transducer； an insertion portion 12 formed in a rigid cylindrical shape in which the holding part is fixedly installed at a distal end； and an insertion assisting instrument 31 that is formed in a rigid rod shape or cylindrical shape, and that is insertedly disposed in a freely insertable/extractable manner in the insertion portion； wherein: the holding part is fixedly installed at the distal end of the insertion portion so as to form a shape that is curved with a predetermined angle in a separating direction with respect to a longitudinal direction from the distal end of the insertion portion； and a curvature angle of the holding part with respect to the longitudinal direction of the insertion portion is set so that, when the insertion assisting instrument is insertedly disposed in the insertion portion, an extension line of a straight line that contacts a distal end face of the insertion assisting instrument contacts the ultrasound transmitting/receiving face.
