A guide assembly for an endoscope includes a shaft sleeve, barrel sleeve, support sleeve and endless track device for propulsion by endlessly moving in an axial direction of an elongated tube. A rotation wheel is supported on the barrel sleeve, for driving the endless track device by rotating. An idler roller is supported on the support sleeve in a rotatable manner, for keeping the endless track device movable in cooperation with the rotation wheel. A small diameter portion is formed with two axial ends of the rotation wheel by decreasing a wheel diameter thereof along a wheel axis, for allowing leaving of the idler roller from the rotation wheel upon rotationally shifting the support sleeve around the barrel sleeve, so that the endless track device is released from tight contact therewith, and separated from the barrel sleeve in the axial direction with the support sleeve.
