Provided is an outer casing having a bottomed tube shape, the casing having a cooling water supply port, and a cooling water discharge port, and being inserted into a high-temperature furnace; an inner casing having a bottomed tube shape inserted into the outer casing; an imaging unit that is disposed in the inner casing which captures an image of the exterior of the outer casing; and partition members that are between an inner surface of the outer casing and an outer surface of the inner casing which define a first flow channel, a second flow channel, and a communicating channel for communicating the first flow channel and the second flow channel between the bottom of the outer casing and the partition members.