To provide a fringe detector capable of fringe detection, with high robustness, not affected by texture and noise.

A matrix producing part 23 produces a two-dimensional matrix for every conversion coefficient obtained by a DCT processing part 22. A normalization part 25 controls the two-dimensional matrix value corresponding to the conversion coefficient indicating AC component based on the standard deviation of the two-dimensional element corresponding to the conversion coefficient indicating DC component among the conversion coefficients. Thus, without being affected by the change of fringe contrast due to the change of illumination intensity and the change of light reflectance at the surface of an inspection object, a fringe characteristic quantity including the fringe direction can be calculated and so the fringe can be exactly detected.