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.