In order to inspect a substrate, an image information of a substrate before applying solder is displayed. Then, at least one inspection region on the substrate is image-captured to obtain an image of the inspection region that is image-captured. Then, image information that is to be displayed is renewed and the renewed image information is displayed. And, in order to inspect a foreign substance, obtained image of the inspection region is compared with a reference image of the substrate. Therefore, an operator can easily catch a region corresponding to a specific region of the image that is displayed, and easily detect a foreign substance on the substrate.