Provided are a structure of molding tools and an injection molding device that can easily perform molding of an optical element even from a resin of low velocity or the like and can suppress any negative effects by air. The structure of the molding tools includes between the molding tools (61, 62) a fixed molding tool (61) and a movable molding tool (62) and an O-ring (63a) for keeping air tightness and a resin seal (63b) for preventing any resin leakage. The O-ring (63a) performs decreasing of the pressure in a cavity (CV) formed by joining the molding tools (61, 62), whereby the vacuum molding in which resin supply and resin curing is carried out under a decreased pressure can be performed. Accordingly, the effects such as prevention of air bubbling due to air trapping by injected resin within the cavity (CV) can be attained. Furthermore, the resin seal (63b) can prevent any resin leakage from the molding tools (61, 62) even when the resin having a low viscosity is used.