According to the method and the apparatus for curing a coated film of the present invention, since an ionization radiation is applied after the O2 concentration in the near-surface layer within 1 mm above the surface of the coated film is adjusted to 1000 ppm or lower, the coated film can be sufficiently cured by irradiation of the ionization radiation. In other words, according to the method and the apparatus for curing a coated film of the present invention, since the O2 concentration in a thin near-surface layer on the surface of a coated film is decreased, the coated film can be sufficiently cured by irradiation of an ionization radiation. As a result, the amount of inert gas supplied upon irradiation of an ionization radiation can be reduced, and downsizing and cost reduction of equipment can be achieved.