A positive electrode active material (1) disclosed herein includes a Ni content lithium complex oxide (2) containing 70 mol% or more of nickel relative to the total of metal elements other than lithium, and a boron element (4). The Ni content lithium complex oxide (2) is in a form of a secondary particle in which primary particles (2a) are aggregated and has a porosity of 2% or more and 10% or less, and inside the secondary particle, a larger space than an average cross-sectional area of the primary particles (2a) does not exist. The boron element (4) is contained by 0.5 to 3 mol% when the total of metal elements of the Ni content lithium complex oxide (2) is 100 mol%.