A positive electrode active material contains a lithium transition metal composite oxide that contains 85% by mole or more of Ni relative to the total number of moles of metal elements excluding Li and at least one metal element M1 that is selected from among Mg, Ti, Nb, Zr and V in an amount of 3% by mole or less relative to the total number of moles of metal elements excluding Li. The ratio of the concentration of metal element M1 contained in the shell of each primary particle of the composite oxide to the concentration of metal element M1 contained in the core is from 1.01 to 20; and at least one metal element M2 of Ca and Sr is on the surface of each primary particle in an amount of 1% by mole or less relative to the total number of moles of metal elements excluding Li.