In a region where an intestine is movable in the abdominal cavity, conventional endoscope apparatus have suffered from a difficulty in moving an endoscope advancing portion toward a deep intestinal portion. An apparatus for advancing an endoscope is provided, which can be easily manipulated to advance medical instruments having endoscopic functions toward a deep portion. The apparatus includes first and second medical instruments, each having, at a distal end portion thereof, a balloon portion that can be fixed to an intestinal wall. In a fixed state, the balloon portion of the first medical instrument is configured to form a gap for enabling a distal end portion of the second medical instrument to advance therethrough. In a fixed state, the balloon portion of the second medical instrument is configured to form a gap for enabling a distal end portion of the first medical instrument to advance therethrough.
