PURPOSE: To provide a mold capable of obtaining moldings with excellent finishing accuracy without causing any deformation or damages of mold by molding objects to be molded at a constant pressure suitable to the molding conditions of the objects to be molded.

CONSTITUTION: In the mold 2, a molding space 5 is defined by a movable side core 7 and a mold plate 8 and a stationary side mold plate 17. In the core 7, a communicating bore 32 is formed which can communicate with the molding space 5 and outer space. A valve unit 31 is detachably secured to the communicating bore 32. The valve unit 31 is provided with an escape valve mechanism and the escape valve mechanism is actuated when pressure in the molding space 5 reaches the preset valve opening pressure, it acts to open the valve 33 and exclude, i.e., resin within the molding space 5 via an escape hole 40 and the communication hole 32 to the outside space.