Abstract: A card output gap adjustment mechanism installed in the casing of a card stacker and controlled to adjust a card output gap through which cards are individually driven out of the casing by a transmission mechanism, the card output gap adjustment mechanism including a back holder having two vertical guide rails and a top through hole, a cover plate covered on the back holder, an adjustment plate moved along the vertical guide rails in the back holder and defining with a pad in the casing the card output gap, the adjustment plate having two vertical sliding grooves respectively coupled to the vertical guide rails in the back holder and a vertical top screw hole, and a rotary adjustment knob inserted through the top through hole on the back holder and threaded into the vertical top screw hole and rotated to move the adjustment plate along the vertical guide rails and to further adjust the pitch of the card output gap.