An insertion assisting device (60) has an insertion path (70) into which an insertion portion (12) of an endoscope (100) is inserted and has a substantially tubular shape. The insertion assisting device (60) includes a ventilation opening (90) that is formed on a distal-end surface or outer circumferential surface thereof, a ventilation duct (74) that communicates with the opening (90) and is different from the insertion path (70), and a liquid reservoir tank (116) that is connected to a base-end side of the duct (74) and stores liquid flowing out of the duct (74). In an alternative embodiment, the ventilation duct is connected to a suction device through a duct provided in the endoscope, thereby reducing the number of cords diverging from the system. Preferably, the ventilation duct is connected to a forceps channel in the endoscope. Preferably, the ducts are inserted in a universal cable extending from the endoscope handle portion.
