A mold apparatus, an injection molding apparatus, and an injection molding method, which can satisfactorily form a preform having a bottom thicker than a body, are provided. The mold apparatus comprises a neck mold, an injection cavity mold, and an injection core mold having an inside core mold and an outside core mold, and further comprises a regulation means, such as an urging member, for regulating the movement of the inside core mold toward the outside of the injection cavity mold.