An endoscope comprising: an operation section provided with an operating member; an insertion section that is provided on a distal end side of the operation section and that is suitable to be inserted into a subject; a treatment tool erecting base provided at a distal end part of the insertion section; a movable member (96, 242) that is arranged to be exposed to the outside of the operation section and that moves in association with an operation of the operating member; a proximal end opening provided in the operation section; a distal end opening provided in the distal end part; an erecting operation wire channel that is provided in the insertion section and that causes the proximal end opening to communicate with the distal end opening; an erecting operation wire (60, 126) that is inserted through the erecting operation wire channel, that has a distal end side which is arranged outside the distal end opening and which is coupled to the treatment tool erecting base, that has a proximal end side which is arranged outside the proximal end opening and which is coupled to the movable member (96, 242), and that is pushed or pulled in accordance with a movement of the movable member (96, 242) to move the treatment tool erecting base; and an attachment member (98,98A,212,234,244) that is provided at a proximal end of the erecting operation wire (60, 126) and that is engaged with the movable member (96, 242) in an attachable/detachable manner by a one-touch operation, wherein the erecting operation wire (60, 126) has a flexible wire body, and a gap filling member that is arranged at at least a portion in an axial direction of the wire body and that is formed to have a diameter larger than an outside diameter of the wire body and smaller than an inside diameter of the erecting operation wire channel; characterized in that the gap filling member is fixed to the wire body of the erecting operation wire (60, 126) and is an outer layer member that is disposed on an outer periphery side of the wire body and that extends in the axial direction of the wire body. an operation section provided with an operating member; an insertion section that is provided on a distal end side of the operation section and that is suitable to be inserted into a subject; a treatment tool erecting base provided at a distal end part of the insertion section; a movable member (96, 242) that is arranged to be exposed to the outside of the operation section and that moves in association with an operation of the operating member; a proximal end opening provided in the operation section; a distal end opening provided in the distal end part; an erecting operation wire channel that is provided in the insertion section and that causes the proximal end opening to communicate with the distal end opening; an erecting operation wire (60, 126) that is inserted through the erecting operation wire channel, that has a distal end side which is arranged outside the distal end opening and which is coupled to the treatment tool erecting base, that has a proximal end side which is arranged outside the proximal end opening and which is coupled to the movable member (96, 242), and that is pushed or pulled in accordance with a movement of the movable member (96, 242) to move the treatment tool erecting base; and an attachment member (98,98A,212,234,244) that is provided at a proximal end of the erecting operation wire (60, 126) and that is engaged with the movable member (96, 242) in an attachable/detachable manner by a one-touch operation, wherein the erecting operation wire (60, 126) has a flexible wire body, and a gap filling member that is arranged at at least a portion in an axial direction of the wire body and that is formed to have a diameter larger than an outside diameter of the wire body and smaller than an inside diameter of the erecting operation wire channel; a flexible wire body, and a gap filling member that is arranged at at least a portion in an axial direction of the wire body and that is formed to have a diameter larger than an outside diameter of the wire body and smaller than an inside diameter of the erecting operation wire channel; characterized in that the gap filling member is fixed to the wire body of the erecting operation wire (60, 126) and is an outer layer member that is disposed on an outer periphery side of the wire body and that extends in the axial direction of the wire body.