A guide assembly for an endoscope having an elongated tube includes a first inner sleeve, a first outer sleeve, an endless track device, engagement rollers, a second inner sleeve and idler rollers. The endless track device has an annular surface, is supported around the first outer sleeve, for endlessly moving in an axial direction of the elongated tube in contact with a wall of the body cavity, for propulsion of the elongated tube. A setting device as second outer sleeve is shiftable between a set position and a release position, for pressing the idler roller on the engagement roller when in the set position, to nip the endless track device therewith, and for retracting the idler roller from the engagement roller in an outward direction when in the release position, to facilitate removal of the endless track device from the first outer sleeve.
