A self-propelled type of guide assembly for an endoscope includes a barrel for receiving an elongated tube of the endoscope in an axial direction. A rubber ring retains the barrel to the elongated tube in a form with a clearance space defined between the barrel and the elongated tube. The barrel includes a barrel sleeve, having a first inner diameter according to an outer diameter of the elongated tube. An end cup is formed to extend from an end of the barrel sleeve, has a second inner diameter larger than the first inner diameter, for allowing the steering device in the elongated tube to steer. Furthermore, a movable endless track device has an annular surface, movable on an endless track outside the barrel, for pushing a wall of a body cavity for propulsion in the axial direction. A drive roller moves the endless track device relative to the barrel.