A propelling device includes a traveling body that rotates in a state of being brought into contact with an inner wall of an alimentary canal, an external cylinder around which the traveling body is wound, and a mounting cylinder on which a tip end portion of an endoscope is mounted. Three driven rollers are rotatably attached to the external cylinder. The traveling body is pinched between the driven rollers and driving gears. As the driving gears rotate, the traveling body travels in a circulating manner. A rotating shaft of the driven roller located at the center among the three driven rollers is held by a shaft hole that is made long in a gear arrangement direction in which the driving gears are disposed side by side.