To provide a marking device using a laser beam, which can prevent the adherence of dust on a convergent lens unit despite a simple construction without the limitation of a scanning range of the laser beam and, at the same time, can remove dust that occurs and floats on a marking area.

A convergent lens unit is mounted on a window 13 provided on a bottom face 12 of a casing 11. An ionizer 14 which generates an air stream across the window 13 and a flow direction changing wall 16 which changes the flow direction of the air stream from the ionizer 14 after passing across the window 13 toward a marking area of a workpiece are provided so as to face each other with the window 13 located therebetween. In the flow direction changing wall 16, a flow direction changing surface 16a which receives the air stream after passing across the window 13 is inclined so as to be enlarged toward the workpiece W.