1. A character noise eliminating apparatus comprising: a character noise area determining device which generates a binary image and determines the character noise area depending on the generated binary image; a density conversion area determining device which sets a plurality of density conversion areas inside and outside the character noise area, wherein the plurality of density conversion areas are only areas adjacent to the determined character noise area; a density converting device which sets, as a reference area of a target pixel, a neighboring pixel group within the same density conversion area as the density conversion area to which the target pixel belongs, and which generates a density converted image by applying local image enhancement; and an image synthesizing device which generates a synthetic image, from which background character noise from a fingerprint or a palm print image is eliminated, based on the density converted image.