To provide a combination structure or the like capable of easily mutually removing two members that are internally sealed by being screwed with each other.SOLUTION: A combination structure combines a first member and a second member by fastening a first screw part that the first member comprises, including a first screw thread and a screw groove corresponding to the first screw thread, with a second screw part that the second member comprises, including a second screw thread and a screw groove corresponding to the second screw thread, by mutual screwing. Therefore, a sealing member is pressed by a portion around a hollow part that the second member comprises, on a second surface that the second member comprises, and a first surface that the first member comprises, opposite to the peripheral portion in such a manner that a clearance gap is not generated between the peripheral portion and the sealing member and between the first surface and the sealing member. In a state of the screwing, a space connecting the second surface with the hollow part is formed between both the screw parts.SELECTED DRAWING: Figure 1
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