Abstract: A mask distance a is adjusted with magnification control unit and mask-shift servo-control unit, and a base plate distance b is adjusted with focus control unit, AFC control unit and table-shift servo-control unit, so that a/b is kept constant, and 1/f=1/a+1/b is satisfied. Even when a focal distance of projection lens fluctuates from temperature change of projection lens due to laser beams, projection magnification is able to be kept constant and focusing is precisely carried out upon imaging mask on the base. The invention is usable for ELA (excimer laser anneal) apparatus of SLS (Sequential Lateral Solidification) type.