Provided is a defect detection device (1) by which it is possible to measure the volume of surface defects with high accuracy. The defect detection device (1) is provided with the following: an image pickup device (3) for picking up an image of an object to be detected; a binarization processing unit (11) for calculating first and second sizes of the same defect in the image by performing first and second binarization processing on the image using first and second binarization threshold values that differ from each other; a ratio calculation unit (12) for calculating a first ratio of the second size to the first size; and a depth determination unit (13) for determining the depth of the defect according to the first ratio.
