To carry out colon endoscopy easily, safely, and quickly by a doctor without requiring long training time by inserting a colon endoscope smoothly and safely into the deepest part of the ascending colon from the sigmoid colon acting as the free intestine via the transverse colon also acting as the free intestine.

A negative pressure-supplying unit which has a tapered shape opening toward the back end of the body of the colonoscope and is swollen outward from the side of the body of the colonoscope, has a negative pressure-supplying hole opening toward the back end of the colonoscope and a negative pressure-supplying channel for supplying negative pressure into the colon via the negative pressure-supplying hole. When the colonoscope is inserted into the colon, negative pressure is supplied from the negative pressure-supplying channel toward the back end of the colonoscope via the negative pressure-supplying hole so that the inside of the colon is evacuated. Thus, the colon wall closely adhers to the outer side of the body of the colonoscope.