PURPOSE: To obtain a molding die having a sliding mechanism, the structure of which is simple and the cost of which is favorable, by a structure wherein a slide core, which is connected with a driving means consisting of a shape memory alloy, and a heating means to heat the driving means are provided.

CONSTITUTION: Molding is done by pouring synthetic resin 17 in a cavity 16, which is formed by a top force 10, a bottom force 11 and a slide core 13 con nected with a spring made of shape memory alloy. In addition, a cylindrical heater 21 is arranged outside the spring 20. According to structure as mentioned above, the slide core 13 is shifted with the shape memory alloy spring 20 by heating the spring 20 with a heater 21 after the opening actions of the top force 10 and of a front force 12. Thus, the driving mechanism consisting of a simple structure for the slide core 13 is obtained. The number of parts of the resultant driving mechanism is small and its structure is simple.