A wafer bonding apparatus including a first stage having a first surface and being configured to hold a first wafer on the first surface; a second stage having a second surface and being configured to hold a second wafer on the second surface facing the first surface; a first target image sensor on an outer portion of the first stage; a second target image sensor on an outer portion of the second stage; and a target portion on the first or second stage, the target portion having a target plate fixedly installed and spaced apart from the first or second target image sensor by a predetermined distance, wherein, in an alignment measurement of the first and second stages, the first and second stages are movable so that the first and second target image sensors face each other and the target plate is between the first and second target image sensors.