A pattern area measuring method includes the steps of: acquiring image data of a pattern; dividing the pattern into partial patterns; calculating the areas of the partial patterns; and calculating the area of the pattern by summing up the areas of the partial patterns. The step of dividing the pattern into partial patterns may further include the steps of: dividing the pattern into fan-shaped partial patterns each having a central angle of a predetermined value; calculating the line profile on a line intersecting the center of the pattern and an edge of the pattern for each of the partial patterns; creating a differential profile; and detecting an edge position of the partial pattern by use of the line profile and the differential profile and then deriving a radius from the center position and the edge position.