PURPOSE: To reduce deformation of a mold due to injection pressure by forming an incomplete thread at a tip of a bolt for blade latch of a fixed mold and a movable mold so as to prevent scuff of the bolt and use it repeatedly.

CONSTITUTION: A fixed mold 21 and a movable mold 22 of a mold 1 are fixed by ten bolts 17a-17j so as not to separate during conveyance. These bolts are respectively screwed into bushes 20 attached in receive plates 5. Here, a bolt to be used for blade latch of the molds is equipped with an incomplete thread formed at a tip of a screw of the bolt. Or, a line BB' which connects the bolt 17g and the bolt 17d and a line CC' which connects the bolt 17i and the bolt 17b are made to pass through nearly the center of a cavity 15. Or, the coefficient of the linear thermal expansion of the bolt is set to be higher than thermal expansion coefficients of a fixed side clamping plate 1, a fixed side retainer plate 3, and a movable side retainer plate 4.