A second metal mold 15 has a through hole 31 that extends in the movement direction of the second metal mold 15. A first metal mold 14 has an internal threaded portion 34 that extends on a common line with the through hole 31 and has an opening at the surface of the first metal mold 14 facing the second metal mold 15. A bolt 39 formed by a shaft 37 and a head 38 is employed. The shaft 37 is passed through the through hole 31 in such a manner that the head 38 is arranged at the opposite side to the first metal mold 14 with respect to the second metal mold 15, and the distal end of the shaft 37 is located at the same side as the first metal mold 14 with respect to the second metal mold 15. When the second metal mold 15 is held in contact with the first metal mold 14, the bolt 39 is rotated by an electric motor 45 through the head 38. In this manner, an external thread 41, which is formed at the distal end of the shaft 37, is threaded to the internal threads 36 of the internal threaded portion 34. This presses the second metal mold 15 against the first metal mold 14.