An object of the present invention is to provide a lithium secondary battery that has a lithium nickel phosphate compound in the positive electrode, is free of collapse of the crystal structure even at high potentials and is resistant to cycle deterioration. The lithium secondary battery according to the present invention has a positive electrode active material. This positive electrode active material contains a lithium nickel phosphate compound that is represented by the general formula LiNi(1-x)MnxPO4 (wherein 0