To provide a laser beam machining apparatus free from falsely recognizing a height position of a frame body of a chuck table as a height position of a workpiece.

The laser beam machining device includes: the chuck table including a holding part for holding the workpiece and a metal frame body surrounding the holding part; and a detection means which irradiates a measuring laser beam to an upper surface of the workpiece held by the chuck table from right above, and detects the height position of the upper surface of the workpiece by receiving reflected light of the measuring laser beam reflected to right above at the upper surface of the workpiece. The metal frame body is processed to suppress reflection to right above even if the measuring laser beam is irradiated from right above.