A computer is caused to realize: a line drawing data acquisition function to acquire line drawing data to be colored; a size-reducing process function to perform a size-reducing process on the line drawing data acquired to a predetermined reduced size so as to obtain size-reduced line drawing data; a first coloring process function to perform a coloring process on the size-reduced line drawing data based on a first learned model that has previously learned the coloring process on the size-reduced line drawing data by using sample data; and a second coloring process function to perform a coloring process on original line drawing data by receiving an input of the original line drawing data and colored, size-reduced line drawing data as the size-reduced line drawing data on which the first coloring process function has performed the coloring, based on a second learned model that has previously learned the coloring process on the sample data by receiving an input of the sample data and colored, size-reduced sample data as the sample data on which the first coloring process function has performed the coloring.