The sharp, small chip being mixed in the cutting lubricants, it scatters, under bad environment of cutting actual place and the like with the sensor of standard specification, it is not possible possibly to correspond. The pioneer of the edge sensor for the CNC construction machine private machine, [metororu] corresponded to cutting actual place, MT-[TATSUCHISENSA] was sold. Positioning and deficiency inspection etc of tool Air blow is installed in the sensor itself. Air piping just is connected, accumulated in the contact section, the chip is blown off The chip, was developed in order to prevent the fact that invades from the opening of the sensor wire protector, it is the up-to-date type. From the contact periphery, by the fact that the air erupts in circumferential condition, invasion to the sensor of the small chip is prevented.