A shift-register circuit comprises an inverter and first to fourth transistors. The pawl is selectively engaged with a positioning unit in the handle. Cooling portions of the cooling unit are selectively driven on the basis of the detection result. For each operation the stretchable rod will extend to its full extension. A gas having a lower ionization energy than nitrogen, such as for example, helium, may be used in combination with nitrogen to produce a lower power plasma resulting in a steeper concentration curve for nitrogen in the silicon oxide film.