1. An apparatus for inspecting a pattern as formed on a workpiece being tested, said apparatus comprising: a search unit operative to find a plurality of similar neighboring patterns residing around a specific pattern on the workpiece and each having similarity to the specific pattern; a calculation unit operative to obtain a degree of dissimilarity between the specific pattern and each said similar neighboring pattern; a variation evaluation unit operative to exclude an allowable error from the dissimilarity to thereby obtain a local critical dimension (“CD”) error criterion value; and a CD error decision unit operative to determine that a local CD error is present when the local CD error criterion value exceeds a threshold value in case a distance between the specific pattern and the similar neighboring pattern increases.