An endoscope (1) as an insertion device is an insertion device having an insertion portion (2) inserted into a subject from a distal end side in a longitudinal axis direction. The insertion portion (2) is provided on the distal end portion (11), on the proximal end side of the distal end portion, and bends (14) that bends in a first direction in response to a bending operation by an operator； A) a passive bending portion (15) as a first flexible tube portion, which is provided on the base end side and does not bend in response to the bending operation of the operator but passively bends by receiving an external force； The second flexible tube provided on the base end side of (15) has a serpentine tube (13). The passive bending portion (15) has a higher bending rigidity in a second direction orthogonal to the first direction than in the first direction.挿入機器としての内視鏡（１）は、被検体内に長手軸方向に先端側から挿入される挿入部（２）を有する挿入機器である。挿入部（２）は、先端部（１１）と、先端部の基端側に設けられ、操作者の湾曲操作に応じて第１の方向に湾曲する湾曲部（１４）と、湾曲部（１４）の基端側に設けられ、操作者の湾曲操作に応じて湾曲せず外力を受けることにより受動的に湾曲する第１の可撓管部としての受動湾曲部（１５）と、受動湾曲部（１５）の基端側に設けられた第２の可撓管部として蛇管（１３）を有する。受動湾曲部（１５）は、第１の方向よりも第１の方向に直交する第２の方向における曲げ剛性が高い。
