The endoscope 2 A includes a flexible tube portion 3 c provided in the insertion portion 3, a drive motor 45 having a drive shaft 45 a, an insertion assist mechanism portion 30 operated by the rotational driving force of the motor 45, a flexible tube portion 3 c in a state in which the first torsional rigidity in the state of being rotated in the winding direction is rotated in the opposite direction and is rotated by the rotational driving force of the motor 45 to transmit the rotational driving force And a drive shaft 50 set to be higher than the torsional rigidity. In the configuration in which the insertion assist mechanism section 30 selectively performs the first action and the second action requiring a force amount from the first action by the rotational driving force , The insertion assist mechanism section 30 performs the second operation by the rotational driving force that the drive shaft 50 is rotated about the axis in the direction opposite to the winding direction and transmitted.内視鏡2Aは、挿入部3に設けられた可撓管部3cと、駆動軸45aを有する駆動モータ45と、モータ45の回転駆動力によって動作する挿入補助機構部30と、可撓管部3c内に挿通配置されてモータ45の回転駆動力によって回転されて回転駆動力を伝達する、巻回方向に回転された状態における第1の捻り剛性が反対方向に回転された状態における第2の捻り剛性より高く設定した、駆動シャフト50とを有し、挿入補助機構部30が回転駆動力によって第1の動作と第1の動作より力量を要する第2の動作とを選択的に行う構成において、挿入補助機構部30は、第2の動作を駆動シャフト50が軸回りに巻回方向とは反対方向に回転されて伝達する回転駆動力によって行う。
