A molding die apparatus and a method thereof are provided, which ensures for air and gas (or fluid) present in a resin filling space to be exhausted so as to be able to fill molten resin into the cavity smoothly and uniformly thereby enabling production of a high quality molded resin product suitable as an optical disc substrate or the like having optimum optical properties required therefore. The molding die apparatus for obtaining the molded product by injecting the molten resin into a cavity that is formed between dies includes a vacuum apparatus which is disposed in proximity to the cavity, the vacuum apparatus including a vacuum tank, an exhaustion channel and a vacuum valve which controls open and close of a channel between the vacuum tank and the exhaustion channel, and the cavity is exhausted efficiently and rapidly by the vacuum apparatus.