PURPOSE: To surely judge whichever the cutting is good or not and to prevent the cutting defect by providing a detecting means that the cutting state is detected by reciprocating within the prescribed range including a cutting place of metal plate.

CONSTITUTION: A cutting confirming device 60 is provided on a column of a laser beam cutting machine. An air cylinder 63 is attached by making a rod to face downward on the upper position than the metal plate 1 on a machining table in a bracket 62 fixed on a frame 61 of the column. Limit switches 64, 65 detecting the upper limit and the lower limit of the stroke of the rod is provided on the air cylinder 63. The air cylinder 63 of the cutting confirming device 60 confirms whether the cutting is suitably executed by extending the rod downward at just upper the cutting position of the metal plate 1 after the cutting is finished. That is, if the top of the rod can be extended to the downward of the metal plate 1 within the prescribed time with the prescribed thrust at the same position, it is judged that the cutting is suitably executed.