To attain the fast conversion of data with no error by means of an LUT of small capacity by preparing a conversion table in which the difference values are arranged in a where the bits of the same digit are put together in a binary display mode.

An extraction part 13 extracts the representative conversion result data which are set in an entry from the 1st or the 2nd difference bit string that is arranged in the entry received from an entry reading part 12. A bit detection part 14 detects the number of '1' of the 1st or the 2nd partial bit string received from the part 13. A count table storage part 15 stores a count table storing the corresponding relation to the number of '1' when they are shown in binary number. An arithmetic part 16 calculates the conversion result data corresponding to the input of the data converted, based on the number of '1' of the 1st and 2nd partial bit strings received from the part 14 and the representative conversion result data received from the part 13.