US Patent 6921362 Outer sheathed endoscope

A tip end part (22) of an outer sheath (20) is rotatable about an axis in a predetermined range with respect to a tip end part (13) of a flexible insertion portion (11). A channel deformation space (19) which enables a part in the vicinity of the tip end of a channel tube (23) to be rotated with following the rotation while being elastically deformed is disposed. A locking mechanism (18, 28) is engaged or disengaged by rotating the tip end part (22) of the outer sheath (20) about the axis in the predetermined range with respect to the tip end part (13) of the flexible insertion portion (11).