Patent ID: 8920118

Claim:
A casing structure comprising: an annular seal member positioned at a connection portion between first and second casings, the annular seal member configured to keep air-tightness between an internal space formed by connecting the first and second casings to each other and an outside of the internal space; a first screw member which is threaded from the internal space, the first screw member positioned at an inside of the annular seal member in the radial direction, and the first screw member is configured to fasten the first and second casings to each other, wherein the first screw member is configured to add fastening force due to fastening thereof to the annular seal member at the connection portion; and a second screw member which is threaded from the outside, the second screw member positioned at an outside of the annular seal member in the radial direction, and the second screw member is configured to fasten the first and second casings to each other, wherein the second screw member is configured to add fastening force due to fastening thereof to the annular seal member at the connection portion, wherein a head of the first screw member engages with one of the first and second casings, such that the first screw member fastens the first and second casings to each other, and the head is positioned in the internal space.