An over-tube for use in an endoscopic treatment in an abdominal cavity using an endoscope includes an over-tube main body which is inserted from a distal portion thereof via a natural opening in a patient's body to access the inside of the abdominal cavity from the distal portion through a lumen wall, and an internal cover which is disposed in a passage of the endoscope disposed in an inner cavity of the over-tube main body and which is extractable from a proximal portion of the over-tube main body.
