A mover moves an object in a first direction. A plurality of partial images of the object are obtained by switching N (N is a natural number equal to or greater than 2) light sources while moving the object. An image of the object is obtained by deleting a part according to the switching order of the light sources from a composite image obtained by combining the plurality of partial images for each light source. As a result, as many images of the object illuminated only by one of the N light sources as the N light sources, i.e. N images of the object, are obtained.