The present invention enables the desired area on a luminal organ to be held correctly during laparotomy or laparoscopic surgery, even without carrying out dot inking which requires a high degree of skill. In the present invention, a magnetic body is pre-anchored at a specific position inside a luminal organ. During surgery, a magnet is brought close to the outside of the luminal organ, such that the magnetic body is adsorbed to the magnet, along with the body tissue of the luminal organ, enabling traction.