PROBLEM TO BE SOLVED: To provide a guide tube apparatus having a distance measuring portion that changes directions thereof as a bending portion of an endoscope bend.SOLUTION: A tube body has a channel formed by a flexible material and enabling an insertion portion 2 of an endoscope 3 to be inserted therethrough. When a base end side of the tube body is attached to the insertion portion, a tip portion of the tube body is positioned in a tip region R located closer to a tip side than a curved portion 14 of the insertion portion. The tube body has, in the tip region thereof, a transmission portion 41 that transmits electromagnetic wave to a measuring object, a receiving portion 43 that detects electromagnetic wave reflected from the measuring object and a distance measuring portion 39 that measures the distance to the measuring object.
