To solve problems of a conventional paste-like sealer in which since the sealer is applied to a sealed part using a coater and may be subjected further to a finishing operation of wiping the applied sealer with a brush, a worker must perform the application or the like of the sealer in an improper position and tends to be increasingly fatigued with such complicated operation when the sealed part is located in an elevated part or in a narrow space, and a lot of time is further required to ensure the application quality of the sealer.

The sealer 5 for sealing the sealed part 3 is constituted by a sheet-like member formed in a shape according to the three-dimensional shape of the sealed part 3. The sealer is heated while being placed on the sealed part 3, whereby sealing of the sealed part 3 is performed.