Abstract: A digital camera 28 that is capable of color photography and that has an automatic exposure-adjustment function and an automatic focusing function is mounted in such a way that it can be swiveled by means of a tilt device 29 to a prescribed position in relation to a photographed object 30. The digital camera is swiveled by the tilt device such that the center of the screen moves along a predetermined prescribed route 31 a on subject surface 31. Every time the digital camera's field of view reaches a prescribed location on the route, a portion of the subject surface and a portion of a member 35 that is set on the subject surface are photographed by the digital camera as a photographed range. It is desirable to adjust the focal distance of the digital camera such that the image resolution of each photographed range is nearly constant. The photographed member is a liquid gasket that is applied in bead form along the route and that is detected as defective if its width exceeds a prescribed range.