Overtube

An over-tube which guides a device having an insertion section to be inserted into a body of a patient, when inserting the insertion section into or retracting the insertion section from the body of the patient, wherein:

• a gas-supplying passage is defined between an inner face of the over-tube and the device to be inserted into the over-tube;
• the gas-supplying passage communicates with a gas-supplying port which is provided on a proximal end side of the over-tube, and a communicating port which is formed on an over-tube insertion section and supplies a gas into a trachea of the patient;
• and
• a first sealing member which secures and air passage for communicating the gas-supplying passage and the trachea of the patient via the communicating port by sealing between a body wall of the patient and the communicating port, is provided on a periphery of an over-tube insertion section.