An overlapping area between a first defect candidate area and a second defect candidate area is specified as a defect area, the first defect candidate area being detected on the basis of a difference between a value of each pixel in a captured image and a value of a corresponding pixel in a reference image, the second defect candidate area being detected on the basis of a ratio between the value of each pixel in the captured image and the value of corresponding pixel in the reference image. It is therefore possible to accurately detect a defect while detection of false defect is suppressed. In a preferable defect detection part (62), a defect candidate area is detected in a shaking-comparing part (623) on the basis of differences of values of pixels between the captured image and the reference image, and pixels to be used to calculate the above ratio in a misinformation reduction processing part (629) are limited to pixels included in the defect candidate area. Thus, the defect can be detected efficiently.