An upper electrode film includes a first conductive oxidation layer made of an oxide expressed by a chemical formula M.sub.1O.sub.x2, a second conductive oxidation layer made of an oxide expressed by a chemical formula M.sub.2O.sub.y2 and a third conductive oxidation layer. Here, the second conductive oxidation layer is formed to have a degree of oxidation higher than the first conductive oxidation layer and the third conductive oxidation layer, and among the composition parameters x.sub.1, x.sub.2, y.sub.1, y.sub.2, z.sub.1 and z.sub.2, there are the following relations, y.sub.2/y.sub.1>x.sub.2/x.sub.1, y.sub.2/y.sub.1>z.sub.2/z.sub.1, and z.sub.2/z.sub.1.gtoreq.x.sub.2/x.sub.1.