1. A three-dimensional object forming apparatus comprising:a print head configured to discharge a liquid;
an energy-emitting device configured to cure the liquid discharged from the print head and form a dot;
a storage medium that stores a dither mask; and
one or more controllers programmed to:
control an operation of the print head 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, and
determine 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 the dither mask.