1. A defect inspection method for detecting surface errors in a three-dimensional shape, comprising: repetitively scanning a light beam in a linear pattern on a first work; said first work being a reference work having a desired surface shape; storing reference images of said linear pattern on said first work, together with related information about positions of said light beam to produce a first matrix value at each position of said light beam; repetitively scanning said light beam in said linear pattern on a second work; said second work being an inspected work; storing inspected images of said linear pattern on said second work, together with related information about positions of said light beam to produce a second matrix value at each position of said light beam; finding a set of differences between each element of said first matrix and each corresponding element of said second matrix: defining as defect candidates elements of said set of differences in which said difference exceeds a most frequent difference by a predetermined value; and determining a presence of defects based on states of said defect candidates.