Provided is a spinel-type lithium-manganese-containing complex oxide that is related to a 5 V-class spinel, and with which output characteristics and charge-discharge cycle ability can be enhanced while suppressing gas generation. Proposed is a spinel-type lithium-manganese-containing complex oxide comprising at least Li, Mn, O, and two or more other elements, and having an operating potential of 4.5 V or more with respect to a metal Li reference potential, wherein: D50 is 0.5 to 9 μm; a value of (|mode diameter−D50|/mode diameter)×100 is 0 to 25%; a value of (|mode diameter−D10|/mode diameter)×100 is 20 to 58%; a ratio of average primary particle diameter/D50, which is calculated from an average primary particle diameter calculated from a SEM image and the D50, is 0.20 to 0.99; and a primary particle is a polycrystal.