A spatial light modulator has a plurality of grating elements. Each grating element can be switched between a diffracting state and a reflecting state, and only zeroth order light beams from the spatial light modulator are directed onto photosensitive material. An irradiation position on the photosensitive material is moved in a direction perpendicular to a width direction corresponding to an arrangement direction of the grating elements. The minimum line width on the photosensitive material corresponds to a width of a predetermined number of grating elements where the predetermined number is two or more. Each group of grating elements which are spatially continuously in the diffracting state or spatially continuously in the reflecting state consists of the predetermined number of grating elements or more while writing is performed. This makes it possible to appropriately record an image on the photosensitive material at high addressable resolution.