Method and apparatus for reviewing defects on mask

A defect to be reviewed is selected from a plurality of defects obtained from inspection results. When the selected defect is a defect of a pattern written using an iteration expression in design data on the mask, another pattern written using the iteration expression in the design data is extracted. A defect present in another pattern is extracted. A peripheral pattern portion located at the periphery of the selected defect and a peripheral pattern portion located at the periphery of the extracted defect are extracted. It is determined whether the peripheral pattern portions extracted are similar to each other. When the peripheral pattern portions are similar to each other, the selected defect and the extracted defect are grouped. It is determined whether the selected defect is an actual defect or a pseudo defect. The determination result is applied to the other grouped defect.