Apparatus for auto focus control, and method for manufacturing semiconductor device

Auto-focusing device according to one embodiment of the present invention by receiving a reflected light reflected from the inspection surface of the wafer using an optical detector, the light receiving signal for generating a received signal, the drive to decide whether or not to execute the auto-focusing focus error correction, and moves the wafer stage for supporting the wafer, z directions of the wafer stage by the focus error compensation signal to the control unit for generating a signal, received applied to the drive signal, it generates a focus error correction signal and a stage driving unit for adjusting the position. The drive signal includes a whole (on) and the off signal (off) signal, and the OFF signal is characterized by a hold (hold) the z direction position of the wafer stage.