In an exposure device according to the present invention, a plurality of exposure bands each containing multiple dots is formed on photographic paper by repeating main scanning in a main scanning direction based on image data that contains multiple pixels and the transfer of the photographic paper in a sub scanning direction. Of the multiple dots contained in each of two continuous exposure bands, the mean value of the pixel levels of two pixels corresponding to two dots with the same positional relationship for the main scanning direction is calculated to derive interpolation data. Thus, the region between the two dots neighboring in the sub scanning direction on the photographic paper is exposed on the basis of the interpolation data.