Abstract: There is provided a flexible guide tube which guides an endoscope or a therapeutic device into an abdominal cavity through the mouth and stomach to conduct an observation or a therapeutic treatment in the abdominal cavity. The guide tube includes an insertion section which has a distal end, a peripheral section, and a central axis, and which is capable of being inserted into a body through the mouth, and two expandable and shrinkable balloons arranged in the vicinity of the distal end at a predetermined distance from each other in the axial direction on the periphery of the insertion section. The predetermined distance is preferably set to 3 to 8 mm, and the length of the insertion section is preferably set to about 600 to 1000 mm.