A medical method for a lumen of a body includes, introducing a first endoscope and a first overtube up to a strictured area inside the lumen, the first overtube having a first channel having an inner diameter such that the first endoscope can be introduced into the lumen, introducing a second overtube into the lumen by using the first overtube as a guide, the second overtube having a second channel having an inner diameter larger than an outer diameter of the first overtube such that a second endoscope can be introduced into the lumen, the second endoscope having an outer diameter larger than an outer diameter of the first endoscope, removing the first endoscope and the first overtube from an interior of the second channel, inserting the second endoscope into the lumen by using the second channel as a guide, and dilating the strictured area by using the second endoscope.
