To surely make it possible to tightly close an opening part of a dark box by an opening/closing door without being affected by a slide mechanism part.

The laser beam processing device comprises the dark box 1 in which the opening/closing door 12 is provided to the opening part 11 for storing a workpiece 9 and the slide mechanism part 3 to slide a table 31 on which the workpiece 9 is laid to a processing position A inside the dark box 1. The whole of the slide mechanism part 3 is provided inside the dark box 1. Namely, the slide mechanism 3 is made so that only the table 31 is slid to the outside of the dark box 1 via the opening part 11.