1. A phase change random access memory comprising: an under electrode; a first interlayer insulating layer which is formed on said under electrode; an impurity diffusion layer which is embedded into a first pore passing through said first interlayer insulating layer; a phase change recording layer which is formed on said first interlayer insulating layer; an upper electrode which is formed on said phase change recording layer; and an electric field application portion that applies an electric field to said impurity diffusion layer so as to deplete at least a portion of said impurity diffusion layer and decrease an effective diameter of said impurity diffusion layer, wherein an effective diameter of a heat spot that changes a phase state of said phase change recording layer becomes smaller than the diameter of said first pore by applying a current between said under electrode and said upper electrode.