In the present invention, a tip end part 58 of an over tube 50 is made of sponge and is easily enlarged in diameter. When only the insertion section 12 is extracted from the over tube 50, air of a first balloon 30 is released first and the first balloon is deflated. Thereafter, when the over tube 50 is fixed and the insertion section 12 is extracted, the band 45 collides against the sponge tip end part 58 and the sponge tip end part 58 is easily enlarged in diameter. Thereby, the band 45 and the first balloon 30 easily pass through the sponge tip end part 58, and the insertion section 12 is easily extracted from the over tube 50.
