To obtain a laser machined surface of high definition by efficiently covering the reverse side of a machining region of a workpiece by a shielding gas.

A laser beam machining apparatus is provided with: a directivity application means F which is arranged on the reverse side of a machining region of a workpiece 6, which forms gas flows 28, 29 flowing into the reverse side of the machining region of the workpiece 6 from the outer periphery, and which directs the gas flows in a manner covering the reverse side of the laser beam machining region of the workpiece; and a hollow cylindrical body 21 which guides the gas flow 29 covering the reverse side of the laser beam machining region of the workpiece, in a direction receding from the reverse side of the machining region together with spatters generated during the laser beam machining.