A seal mechanism that can prevent the occurrence of corrosion and abnormal discharge. The seal mechanism is disposed between first and second structural members having opposing surfaces. A first seal trench and a second seal trench are formed respectively in a first opposing surface of the first structural member and in a second opposing surface of the second structural member. A first seal member and a second seal member are housed respectively in the first and second seal trenches. The first seal member and the second seal member are brought into pressure contact with each other. These seal trenches have a first seal surface and a second seal surface from which aluminum is exposed, and further have first shut-off surface disposed between the first opposing surface and the first seal surface and a second shut-off surface disposed between the second opposing surface and the second seal surface. The first seal member has a first covering portion that covers the first shut-off surface, and the second seal member has a second covering portion that covers the second shut-off surface.