The present invention provides a nickel atom-, manganese atom- and cobalt atom-containing composite carbonate that is high in specific surface area and large in tap density, and useful as a raw material for producing a lithium nickel manganese cobalt composite oxide to be used in a positive electrode active material for use in a lithium secondary battery, and provides a method for industrially advantageously producing the composite carbonate. The composite carbonate includes nickel atoms, manganese atoms and cobalt atoms, and has an average particle size of 20 μm or more and 40 μm or less, a BET specific surface area of 50 to 130 m2/g and a tap density of 1.7 g/ml or more.