A lithium/nickel/cobalt/manganese-containing composite oxide powder represented by the formula LipNixCoyMnzMqO2-aFa (wherein M is at least one element selected from the group consisting of Al, Ge, Sn, alkaline earth metal elements and transition metal elements other than Co, Mn and Ni, 0.9≦p≦1.1, 0.2≦x≦0.5, 0.2≦y≦0.5, 0.1≦z≦0.4, 0≦q≦0.5, 1.9≦a≦2.1, p+x+y+z+q=2, and 0≦a≦0.02), characterized in that when the powder is classified into small particle size-classified particles with an average particle size 2 μm≦D50≦8 μm and large particle size-classified particles with an average particle size of 10 μm≦D50≦75 μm, the ratio of (% by weight of the small particle size-classified particles)/(% by weight of the large particle size-classified particles) is from 15/85 to 40/60.