A washing instrument for an insertion device performs positioning of a distal portion by an axial direction regulating portion provided in a cylindrical hollow washing instrument main body and abutting on the distal portion of the insertion device, and a rotating direction regulating portion facing an observation surface of the insertion device, thereby attaching the insertion device. A raised distal portion of a swing base received in a receiving chamber of the distal portion abuts on a projecting locking portion provided on an inner peripheral surface between the washing ports, the locking portion and the axial direction regulating portion hold a positioned state of the distal portion, and washing liquids jetting out from the washing ports directly collide with washing target regions of the receiving chamber to perform washing.
