PURPOSE: To assist the smooth insertion of a large intestine fiber scope into the colon by providing the auxiliary implement with a slender balloon-like implement having the cross diameter not exceeding the bore of the colon when the implement is inflated and forming a hole to permit putting in and out of a material in this implement.

CONSTITUTION: The slender balloon-like implement 1 is inserted into the patient's rectum and liquid, gas or solid having a flow property is injected from the hole 2 therein. The slender balloon-like implement 1 extends successively into the intestinal canal according to curving of the intestinal canal, advances beyond the sigmoid colon and arrives at the descending colon at this time. The bar-shaped balloon has the nature that the balloon is soft when inflated insufficiently and is solid and straight when sufficiently inflated and, therefore, the slender balloon-like implement 1 easily advances beyond the sigmoid colon according to curving in the initial period of inflation and, thereafter, straightens the sigmoid colon when the implement is sufficiently inflated. Henceforth, the curving of the other large intestine parts is made dull in the same manner and thereafter the large intestine fiber scope 5 is manipulated to be inserted into the large intestine along the slender balloon-like implement 1.