A cathode with a cathode active material is provided. The cathode active material is obtained by mixing a zirconium-containing lithium cobalt composite oxide containing zirconium as a sub-component element in a first lithium cobalt composite oxide expressed by a formula Li.sub.tCoM.sub.sO.sub.2 (where M is at least one kind of element selected from Fe, V, Cr, Ti, Mg, Al, B, and Ca; 0.ltoreq.s.ltoreq.0.03; 0.05.ltoreq.t.ltoreq.1.15), and a second lithium cobalt composite oxide expressed by a formula Li.sub.xCo.sub.l-yA.sub.yO.sub.2 (where A is at least one kind of element selected from Mg and Al; 0.05.ltoreq.x.ltoreq.1.15; 0.ltoreq.y.ltoreq.0.03).