To secure the air-tightness between the one side and the other side of a partition wall even in the case of penetratingly setting a complexed part which is not sufficiently complexed, into the partition wall.

A preform 6 for complexing in the complexed part 2 is formed as laminated state in the thickness direction of the partition wall 5 with plural layers 7 and also, formed as a skelton structure 9 intricated with each layer 7, and communicated gas holes 11 are formed not only between the skelton structure elements 8 but also, in the inner part of each skelton element 8. Cutting work to this compexed part 2 may be executed from the layer 7b at the one side of the partition wall 5 rather than from the innermost layer 7a at the other side of the pertition wall 5 in plural layers 7 of the preform 7 for complexing. Even in the case of being insufficient to complexing, it is utilized that the continuity of the communicative gas holes 11 is cut off with the interface between the layers 7a, 7b.