The present invention relates to a high-strength aluminum alloy thick plate composed of an aluminum alloy including a prescribed quantity of Si, Mg, Ti, Fe, and the balance Al. The thick plate has a material structure in which an area ratio of Mg2Si having circle equivalent diameters of 3 μm or more in a plate thickness central portion is 0.45% or less; and an area ratio of Mg2Si having circle equivalent diameters of 3 μm or more in a region of 20 mm±1.5 mm from a plate surface in a plate thickness direction is 1.2 times or more and 3.0 times or less the area ratio of Mg2Si having circle equivalent diameters of 3 μm or more in the plate thickness central portion. The aluminum alloy thick plate has sufficient strength and good uniformity of strength in the plate thickness direction, and can be manufactured by cooling it after a solution treatment, so that suitable temperature difference occurs between a plate thickness central portion and a surface, and then performing a quenching treatment.