A three-dimensional object forming apparatus includes: a head unit; a curing unit that cures the liquid discharged from the head unit, and forms a dot; and a forming control unit that controls an operation of the head unit such that a three-dimensional object is formed as an aggregate of dots by representing a shape of the three-dimensional object to be formed as a voxel-set and forming a dot in a voxel of the voxel-set which is determined as a target in which the dot is formed by a determination unit. The determination unit determines a target voxel in which a dot is formed depending on a result of comparing a forming index value which is a value depending on a dot forming rate in a voxel of the voxel-set which is positioned on an inside of the three-dimensional object with a threshold of a dither mask.