To provide an adjustment tool which is used in a cover device for hermetically sealing a pipe penetration part of a wall, having air-tightness and water-tightness under high pressure.

A cover device for hermetically sealing a pipe penetration part of a wall, includes a hermetic seal sheet wound in a cylindrical shape and covering between a pipe opening portion of a sleeve fitted into a through hole of a pipe penetration part of a construction wall and a pipe part of a pipe passing through the pipe opening portion, and is constituted by fixing both cylindrical openings of the cylindrical seal sheet to the pipe part of the pipe. An adjustment tool is used for the cover device and is arranged between both cylindrical openings of the hermetic seal sheet and the pipe part of the pipe. The adjustment tool has a cylindrical shape and includes a first layer including a polymer and a second layer including ceramics, an inner periphery of which contacts with an outer periphery of the first layer.