1. An apparatus for examining an anterior-segment of an eye comprising: a) a projection optical system for projecting slit light onto the anterior-segment, having an optical axis of projection; b) an image-pickup optical system for picking up a cross-sectional image of the anterior-segment which is optical-sectioned by the projected slit light, having an optical axis of image-pickup inclined toward the projection optical axis, and comprising an image-pickup lens and an image-pickup device both being arranged based on the Scheimpflug's rule; c) rotation means for rotating the projected slit light and the image-pickup optical system about the projection optical axis; and d) display means for displaying a three-dimensional image of the anterior-segment based on the cross-sectional images picked up at a plurality of angles and the image-pickup angles corresponding to the images.