A propulsion assembly includes a support sleeve for mounting on a tip device of an endoscope. An endless track device is supported on the support sleeve in an endlessly movable manner, for contacting a wall of a body cavity, for propulsion of the tip device relative to the body cavity. A drive sleeve drives the endless track device. First and second torque wire devices have proximal and distal end portions, the proximal end portion being rotated by a motor, the distal end portion actuating the drive sleeve. Plural helical windings of a first group constitute the first wire device, and are so wound as to increase tightness thereof upon moving the endoscope in a distal direction. Plural helical windings of a second group constitute the second wire device, and are so wound as to increase tightness thereof upon moving the endoscope in a proximal direction.
