A seal structure includes an elastic body and a cap which are located in a boundary between a first component and a second component that seal and define a gas flow path. The flow path is defined by a first through hole in the first component and a second through hole in the second component, the elastic body has a loop-shaped second opening which overlaps with a first opening of the first through hole, and the cap covers the elastic body such that the first opening, the second opening, and a third opening of the cap overlap with each other. The cap is fitted into a groove in the first surface and is in close contact with the second surface. The cap and second component are in close contact with each other to have slidability.