To provide a sealing device for leak inspection which can airtightly seal the same area with the practical seal position of a body to be inspected requiring a high-precision leak test, prior to the leak test and can speedily be attached to and detached from the body to be inspected.

This sealing device 1A for leak inspection is equipped with a cylinder 2, having a passage 20 linked with the inside of the body 9 to be inspected with has a cylindrical tip part 90, a gripping part 23 which is detachably mounted on the outer periphery 92 of the cylindrical tip, and a sealing part 24 which airtightly seals the outer periphery 92 of the cylindrical tip; pistons 3A and 4 which are put airtightly in the cylinder 2 and move between the mounting-time stop positions where the grip part 23 is mounted on the cylindrical tip part 92 of the body 9 to be inspected and the sealing part 24 is pressed against the sealing positions by pressing the grip part 23 and sealing part 24 along an axis P and the non-mounting-time stop positions, where the grip part is demounted; and energizing means 5, which makes the pistons 3A and 4 return to the stop positions at non-mounting time; and an operating means 6 which holds the pistons 3A and 4 at the mounting-time stop position positions and releases them.