A substrate bonding apparatus for use in fabricating LCD devices substantially prevents substrates held to upper stages from sagging. The substrate bonding apparatus may, for example, include upper and lower stages having a plurality of passages for holding respective substrates; suction force applying means having one end mounted within each passage for transmitting a suction force to operably proximate portions of a substrate, wherein the one end of the suction force applying means is projectable from within each passage to a predetermined distance from the stage; and a vacuum pump for providing a suction force to the suction force applying means.