A pattern defect detection method capable of detecting a pattern defect of a semiconductor integrated circuit with higher accuracy is disclosed. The pattern defect detection method includes: extracting an image of an inspection target pattern from an image of a specimen; identifying a reference pattern from design data, the reference pattern having the same shape and the same position as those of the inspection target pattern; calculating a brightness index value indicating a brightness of an entirety of the inspection target pattern; repeating said extracting an inspection target pattern, said identifying a reference pattern, and said calculating a brightness index value, thereby building mass data containing brightness index values of inspection target patterns and corresponding reference patterns; determining a standard range of brightness index value based on the brightness index values contained in the mass data; and detecting a defect of the inspection target pattern based on whether or not the calculated brightness index value is within the standard range.