PROBLEM TO BE SOLVED: To provide a field securing instrument which secures a visual field of a surgical site and an operative field in NOTES (Natural Orifice Transluminal Endscopic Surgery), and to provide an endoscope with the instrument.SOLUTION: The instrument 10 for securing a field is used in the natural orifice transluminal endoscopic surgery, and includes a cylindrical body part 11 with a hollow space. The hollow space in the body part 11 has a cross section formed so as to be larger than the cross section of a shaft 2 of an endoscope 1. The body part 11 can be expanded/contracted in a direction crossing the center axis CL of the hollow space. When the body part 11 is projected from the leading end part of an outer cylinder 5 and expanded, the visual field of the endoscope 1 or the operative field for the operation using the endoscope 1 can be secured by the body part 11. Since the body part 11 can be moved to a place for the operation etc., while the body part 11 is housed in the outer cylinder 5, if the body part 11 is formed in a size to house the body part 11 in the outer cylinder 5 when the body part 11 is contracted, the body part 11 can be easily moved to a place for the operation etc.
