Abstract: The present disclosure relates to a defect inspection device including: an imaging part that captures an image of a first frame having a predetermined width and a predetermined length along a width direction and a length direction of a test object, respectively; an image division part that divides the image of the first frame of the test object captured by the imaging part into a plurality of second frames smaller than the first frame along the width direction of the test object; a brightness calculation part that measures a brightness value of each of the plurality of the second frames, and calculates a defect determination value of the first frame based on the brightness values of the plurality of the second frames; and a control part that determines a line defect existing along the length direction of the test object based on the calculated defect determination value of the first frame.