of the nitrogen injection by the downward nitrogen injector 9 will be described as shown in fig4 when the glass substrate 100 comes in the working area w from the left side in the figure the downward nitrogen injector 9 injects the nitrogen to the side opposite to the advancement direction d of the glass substrate 100 therefore the nitrogen is sufficiently supplied to the glass substrate 100 early after the glass substrate 100 comes in the working area w the downward nitrogen injector 9 on the right side in the figure in the working area w injects the nitrogen in the same direction as the advancement direction of the glass substrate the nitrogen injected from the nitrogen injector 6 and the downward nitrogen injector 9 flows to the outside of the glass substrate 100 along the gap between the upper surface of the glass substrate and the nitrogen injector 3 further the lower surface of the glass substrate 100 is supported by the nitrogen injected from the stage 3 b in a floating and contactless manner the lower surface of the glass substrate 100 is filled with the nitrogen similarly to the upper surface as described above the nitrogen injected from the nitrogen injector 6 and the downward nitrogen injector 9 is positioned so as to accord with at least the whole or part of the injection nitrogen from the stage 3 b and the vicinity of the laser emitter 5 is filled with the.