A lower electrode layer 2, an upper electrode layer 4 formed above the lower electrode layer 2, and a metal oxide thin film layer 3 formed between the lower electrode layer 2 and the upper electrode layer 4 are provided. The metal oxide thin film layer 3 includes a first region 3a whose value of resistance increases or decreases by an electric pulse that is applied between the lower electrode layer 2 and the upper electrode layer 4 and a second region 3b arranged around the first region 3a and having a larger content of oxygen than the first region 3a, wherein the lower and upper electrode layers 2 and 4 and at least a part of the first region 3a are arranged so as to overlap as viewed from the direction of the thickness of the first region 3a.