A holding mechanism 500 has holding portions 501,503. The holding portion 501 holds a part 301a which is exposed to the outside of an endoscope 10. The holding portion 503 is disposed at a position different from that of the holding portion 501. The holding portion 503 holds another part 301b which is exposed to the outside of the endoscope 10, in an orientation different from an orientation of the holding portion 501.