An ileal-mucosa ablation treatment method including: setting a length of a treatment area in an ileal mucosa, wherein the length of the treatment area is set on the basis of at least one of patient characteristics and pathophysiological conditions； marking an end point of the treatment area in the ileal mucosa； and performing ablation treatment on the ileal mucosa, wherein, in the performing ablation treatment, ablation treatment is performed on the ileal mucosa from a start point to the end point while changing treatment positions toward the end point from the start point, and the start point is at a position that is separated from the end point in a longitudinal direction of the ileum by the set length.
