An insertion device includes an operation unit that is operable a traction member configured to apply a traction force to the operation unit, a channel member in which the traction member is inserted the channel member, a tubular seal member fixed to each of the channel member and the traction member and configured to deform along with a movement of the traction member and watertightly separate an interior of the channel member from a part of the traction member, a connecting member configured to clamp one end of the seal member with the part of the traction member, and a fixing member configured to fix the connecting member and the traction member in a state in which the seal member abutting against the connecting member and the traction member is pressed in the longitudinal axial direction.
