To prevent a product from being damaged by turning OFF the arc generation command when the remaining movement amt. of a work is below the reference value.

In a plasma machine 1, a working head 5 provided with an electrode 3 is fixed to a frame 7. A work W to be worked is moved by driving means such as motors 15, 21 and cut. The arc is outputted by an arc generating device 23 from the electrode 3 toward the work W. The remaining movement amt. of the work W is monitored by a monitoring device 27 using X, Y axis driving motors 15, 21, etc., of the driving means. The actual remaining movement amt. of the work W is compared with the preset reference value for judgment by the monitoring device 27. When the actual remaining movement amt. of the work W is below the reference value, the generation command to be transmitted to the arc generation device 23 is turned OFF by a switching means 29. The arc can be prevented from actuating to a product when the actual remaining movement amt. of the work is below the reference value.