To provide structure of fastening portion of a mold that does not require parts precision exactly, to reduce parts cost, to prevent the position displacement caused by transportation or the like, and to improve workability of press fitting and assembling work.

A U-shaped locking portion 4 locking a sheet metal nut 10 has a gap in which the nut 10 moves freely, a projection is put on the bottom surface of the nut 10, and a recess 5 is placed on the mold surface to be engaged with the projection 13 at a position in which the nut 10 is contained in the locking portion 4.