A catheter includes a first structure having an elongated catheter body with at least one lumen and a first connection portion. The catheter includes a second structure that has a second connection portion which is connectable to the distal side of the first connection portion and a third structure that has an inner tube in which an elongated imaging core having an image capturing unit for capturing an image is positionable and a third connection portion which is connectable to the proximal side of the first connection portion. The catheter includes a first prevention portion to prevent the first connection portion from connecting to the third connection portion when the first and second connection portions are connected and a second prevention portion to prevent the first connection portion from connecting to the second connection portion when the first and third connection portions are connected.
