An image processing method which corrects a 3-dimensional CT data value obtained from a 3-dimensional object is provided. The image processing method comprises: a threshold setting step of setting a threshold value used for generating a correction value from the 3-dimensional CT data value obtained from the 3-dimensional object; an average calculating step of calculating an average value of a 3-dimensional CT data block comprising a 3-dimensional CT data element of a correction target and a plurality of 3-dimensional CT data elements in a neighborhood of the 3-dimensional CT data element of the correction target; and a correction step of correcting the 3-dimensional CT data value by using the threshold value set in the threshold setting step and the average value obtained in the average calculating step.