1. A method of measuring pattern dimensions, comprising the steps of: evaluating a relationship between cross-sectional shapes of a pattern and measurement errors of a pattern in a specified image processing technique; and conducting an actual measurement in which dimension measurement of an evaluation objective pattern from image signals of a microscope is carried out, and revising errors of the dimension measurement of the evaluation objective pattern based on the relationship between the cross-sectional shapes of a pattern and the measurement errors of a pattern previously evaluated.