FLAW DETECTOR, AND FLAW DETECTION METHOD

PROBLEM TO BE SOLVED: To suppress the reduction in defect detection accuracy even when a noise area where a signal caused by a factor other than defects occurs is included on an inspection surface and, in particular, the noise area has a two-dimensional distribution.SOLUTION: A flaw detector 1 includes: a first storage unit 11 in which an evaluation object signal of a plurality of scanning lines on an inspection surface is stored; a second storage unit 12 in which a comparison signal to be compared with the evaluation object signal is stored; a representative value determination unit 13 which determines representative values per scanning line with respect to the evaluation object signal and the comparison signal; a scanning line association unit 14 which determines a scanning line of the comparison signal associated with each scanning line of the evaluation object signal; a subtraction signal generation unit 15 which aligns the evaluation object signal and the comparison signal in associated scanning lines, in a scanning direction to generate a subtraction signal; and a defect detection unit 16 which detects a defect by using the subtraction signal.