Positive electrode active material for secondary battery and secondary battery

A positive electrode active material for a secondary battery, comprising

• a lithium metal composite oxide having a crystal structure based on a rock salt structure belonging to the space group Fm-3m,
• wherein the lithium metal composite oxide contains a cation element and an anion element including at least oxygen,
• the cation element includes lithium and a first metal element other than the lithium,
• the first metal element includes at least one element A1 selected from the group consisting of Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb, Sb, and W,
• the content of the element A1 in the lithium metal composite oxide is 10 ppm by mass or more and 1000 ppm by mass or less with respect to a total amount of the lithium metal composite oxide, and
• a mole ratio of the cation element other than the element A1 to the anion element is larger than 1.