NOVELTY - A positive electrode active material comprises main crystal phase consists of lithium (Li)-containing transition metal oxide with a spinel-type structure while containing manganese (Mn) and suboxide with elementary composition different from Li-containing transition metal oxide but with same oxygen arrangement. Element in main crystal phase and element in suboxide exist at 1st region (2) and/or 2nd region (3asterisk3aasterisk3b), wherein 1st and 2nd regions adjoin, and area of 1st region and area of 2nd region are nano-square-meter-orders.    USE - A positive electrode active material for non-aqueous electrolyte secondary battery (claimed) used for electric vehicle, hybrid vehicle, and electrically driven 2-wheeled vehicle.    ADVANTAGE - Elution of Mn is reduced, cycling characteristics, such as longer life of non-aqueous electrolyte secondary battery, are improved, deformation of crystal particle group is suppressed, and reduction in discharge capacity is prevented.    DETAILED DESCRIPTION - A positive electrode active material comprises main crystal phase consists of lithium (Li)-containing transition metal oxide with a spinel-type structure while containing manganese (Mn) and suboxide with elementary composition different from Li-containing transition metal oxide but with same oxygen arrangement. Element in main crystal phase and element in suboxide exist at 1st region (2) and/or 2nd region (3asterisk3aasterisk3b), wherein 1st and 2nd regions adjoin, area of 1st region and area of 2nd region are nano-square-meter-orders, and concentrations of same kind of element differ in 1st region and 2nd region. An INDEPENDENT CLAIM is included for a non-aqueous secondary battery with positive electrode, negative electrode, and non-aqueous ion conductor.    DESCRIPTION OF DRAWING(S) - The drawing shows a top view of a non-aqueous secondary battery with a positive electrode active material.    Positive electrode active material (1)    1st region (2)    2nd region (3asterisk3aasterisk3b)    3rd region (4asterisk4aasterisk4b)