To provide a positive electrode material having 5 V solid phase redox potential comprising spinel structure manganese iron lithium base composite oxide capable of controlling expansion and contraction by using Fe as a replacing element of Mn.

In a secondary battery comprising a positive active material, a negative active material, and a nonaqueous electrolyte containing a lithium salt, the positive active material is spinel structure manganese iron lithium composite oxide having a lattice constant (a) of 8.19-8.28 , represented by general formula, Li[Fe1/2+xMeyMn3/2-x-y]O4 (wherein 0<x, 0<y, x+y=≤1/2, Me is one or two or more of Cr, Co, and Al). The positive active material is prepared in such a way that at least one of a Cr source compound, a Co source compound, and an Al source compound is added to a mixture containing LiOH, MnOOH (manganite), and FeOOH (goethite), the mixed powder is pressed to form a pellet, the pellet is preliminarily baked in the air at 250-600°C for 2-12 hours, the preliminarily baked material is crushed, the crushed powder is molded in a pellet again, then the pellet is heated in the air at 700-850°C for 2-24 hours as main baking.