To provide a masking device which can prevent significant reduction in suction force by magnetic force between a lid and a body even if blasting is performed.

Even if the magnetism of a body 10 deteriorates by blasting, the deterioration in magnetism of the body 10 can be compensated and restored by additionally arranging a magnetic force-reinforcing plate 30 on the bottom 10b of the body 10. Thus, since the masking device 100 can be repeatedly used many times, the necessity for newly manufacturing the same can be extremely reduced. This can suppress an increase in the man-hour by the re-setup of the set of the masking device 100 and the cost by the manufacture of a new masking device 100, in a trial production facility, a production facility, and the like. Further, the period from the deterioration of magnetism to the renewal thereof can be shortened because of the configuration in which the magnetic force-reinforcing plate 30 is attached to the body 10.