To provide a method of automatically detecting a measuring error of a measuring apparatus which can automatically judge whether an error is contained in a measured CD value.

The method comprises step 100 of displaying a pattern image of specified portions of a wafer on a monitor, step 110 of measuring the distances between a plurality of points of the image displayed on the monitor, step 120 of calculating a mean value and a value R2 by utilizing the distances between the plurality of points, step 130 of judging whether the value R2 is less than a set critical value, step 140 of judging that a CD measurement error occurs if the value R2 is judged to be less than the critical value in step 130 and displaying an error on the monitor, and step 150 of displaying the mean value and the value R2 on the monitor if the value R2 is judged to be not less than the critical value in step 130.