An insertion aid including a long guide portion arranged relatively movable in a longitudinal direction along an insertion portion of an endoscope to be inserted into a subject, the guide portion being able to undergo a state change between a first state where flexural rigidity is low, and a second state where flexural rigidity is high, wherein the guide portion includes a strength variable member arranged to extend along a longitudinal direction of the guide portion and whose strength varies according to temperature, and wherein a flexural rigidity of a proximal end side of the guide portion is set to be relatively higher than the flexural rigidity of a distal end side by setting a boundary temperature at which a proximal end side of the strength variable member starts hardening to be relatively lower than the boundary temperature of a distal end side of the strength variable member.
