Various embodiments are provided to reduce a processing time taken when plural bit lengths each assigned to plural strings are converted into plural codes. In one exemplary embodiment, in response to input of the plurality of bit lengths, a number of strings assigned each of the bit lengths, a bit length assigned to each of the strings, and a sequence number of each string in a group of strings assigned each of the bit lengths are recorded. A plurality of base codes are generated on the basis of the numbers of the strings recorded by the recording unit, the base codes each being a code used as a base for codes having the same one of the bit lengths. A plurality of codes is generated by performing in parallel a plurality of processes respectively for the plurality of strings.