Reliability of a decoded result on a barcode is improved without increasing a processing load and a processing time. While a medium transfer mechanism transfers a recording medium, an image capture section captures an image of a surface of the recording medium, and the image data captured is saved in an image memory. Next, a scanning line setup section sets a plurality of scanning lines for image data of a barcode, and meanwhile a decoding section decodes the barcode by making use of image data corresponding to the scanning lines. Subsequently, a judgment section calculates reading reliability according to the image data corresponding to the scanning lines, and makes a judgment on a scanning line having a highest reliability among the reading reliability values. Then, a decoded result for the scanning line corresponding to the judgment result is defined as decoded information for the barcode.