An endoscope as an insertion device includes an insertion portion configured to be inserted into a subject from a distal end side in a longitudinal axis direction. The insertion portion includes: a distal end portion； a bending portion provided on a proximal end side of the distal end portion and configured to bend in a first direction according to a bending operation by an operator； a passive bending portion as a first flexible tube portion provided on a proximal end side of the bending portion and configured to passively bend by receiving an external force without being bent by the bending operation by the operator； and a corrugated tube as a second flexible tube portion provided on a proximal end side of the passive bending portion. The passive bending portion has higher bending rigidity in a second direction orthogonal to the first direction than in the first direction.
