PURPOSE: To provide an auxiliary tool for an endoscope for the large intestine by which the endoscope can be inserted and pulled out in a short time and without giving any pain to a patient and time for inspection is completed with about 15 min by using an extremely simple structure.

CONSTITUTION: An endoscope inserting-through part 12 wherein both ends are opened along its long direction is formed at the central part of a soft tube 11 and a liq. injection pipe 15 communicated with this part 12 is fixed on one end of the soft tube 11 and a reinforcing coil 13 is provided on the inner wall of the endoscope inserting-through part 12 and while this auxiliary tool 10 for the endoscope for the large intestine is inserted into a sigmoid colon of the large intestine, water is injected into the soft tube 11 to expand the tube and to make the sigmold colon straight.