Abstract: An apparatus for processing a signal for aligning a first object having at least one standard mark thereon with a second object having at least one reference mark thereon, includes a first sensor for sensing the standard mark, second sensor for sensing the reference mark through the first object, an illumination source for illuminating the standard mark and the reference mark, a first extracting circuit for extracting a signal concerning the standard mark from the signal stream of the first sensor, a second extracting circuit for extracting a signal concerning the reference mark from the signal stream of the second sensor, and a signal composing circuit for composing the signal concerning the standard mark and the signal concerning the reference mark.