Auxiliary agent (30), it include: tool body (31) for mounting and dismounting optics adapter for endoscope, for receiving (10) that are mountable to and remove from distal portions (11) endoscope (2) of insertion section with earth-retaining optics adapter (20) Adapter latching portion (33a, 36,43) and optics adapter (20), it is contained in tool body (31), locks the optics adapter (20) and is installed to and dismantles from distal portions (11) by the vertical direction optics adapter (20) in the direction of pressing optics adapter (20) Component (33,39,46) is used to adapter retaining section.
