A data correcting apparatus is for correcting drawing data representing a drawing pattern included in a quadrangular drawing area of a drawing subject. The correction process is based on an ideal position and an actual position of the drawing area on the drawing subject. An actual outline is an outline of the drawing area in the actual position, and an ideal outline is an outline of the drawing area in the ideal position. The data correcting apparatus includes a first data corrector that corrects the drawing data to be first corrected drawing data. A first corrected outline is an outline of the drawing area represented by the first corrected drawing data, and is a parallelogram which has two neighboring sides that are the same as the sides of the actual outline. Further, the parallelogram has a shape closer to that of the ideal outline than the actual outline.