An endoscope to be used in combination with an overtube that has a distal end, a proximal end, and a longitudinal axis and holds a treatment tool and an endoscope so as to be movable forward and backward in a direction of the longitudinal axis, the overtube having a movable body that is provided within the overtube and is movable in the longitudinal axis direction inside the overtube, an endoscope holding part that is provided at the movable body and holds the endoscope, and a treatment tool holding part that is provided at the movable body and holds the treatment tool, the endoscope having an insertion part which is insertable into the overtube and has a distal end, a proximal end, and a longitudinal axis and that is locked to the movable body by the endoscope holding part, the endoscope comprising: a first insertion part (150, 172) that is provided on a distal end side of the insertion part; and a second insertion part (151, 173) that is provided on a proximal end side of the first insertion part (150, 172) and has an external diameter larger than that of the first insertion part (150, 172); characterized by said movable body being metallic, and said second insertion part (151, 173) comprising a held part that (153, 170) is provided from a distal end of the second insertion part (151, 172) toward a proximal end side thereof, is held by the endoscope holding part, and has at least a surface formed of an insulating member having an insulation property. a movable body that is provided within the overtube and is movable in the longitudinal axis direction inside the overtube, an endoscope holding part that is provided at the movable body and holds the endoscope, and a treatment tool holding part that is provided at the movable body and holds the treatment tool, the endoscope having an insertion part which is insertable into the overtube and has a distal end, a proximal end, and a longitudinal axis and that is locked to the movable body by the endoscope holding part, the endoscope comprising: a first insertion part (150, 172) that is provided on a distal end side of the insertion part; and a second insertion part (151, 173) that is provided on a proximal end side of the first insertion part (150, 172) and has an external diameter larger than that of the first insertion part (150, 172); characterized by said movable body being metallic, and said second insertion part (151, 173) comprising a held part that (153, 170) is provided from a distal end of the second insertion part (151, 172) toward a proximal end side thereof, is held by the endoscope holding part, and has at least a surface formed of an insulating member having an insulation property. a first insertion part (150, 172) that is provided on a distal end side of the insertion part; and a second insertion part (151, 173) that is provided on a proximal end side of the first insertion part (150, 172) and has an external diameter larger than that of the first insertion part (150, 172); characterized by said movable body being metallic, and said second insertion part (151, 173) comprising a held part that (153, 170) is provided from a distal end of the second insertion part (151, 172) toward a proximal end side thereof, is held by the endoscope holding part, and has at least a surface formed of an insulating member having an insulation property.