The present invention provides an inspecting method and an apparatus therefor. A light illuminates an object to be inspected having optical diffusive characteristics such as a ceramics plate. A part of the light diffuses in the object from an illumination area is reflected at or passes through a defect such as a crack and reaches an imaging area. An image sensor detects the image of the imaging area. A signal showing a larger change is processed thereby to inspect the defect. The object is displaced stepwise relative to the light source and the image sensor. Thus, a crack or the like in an object can be inspected with high accuracy and at a high speed.