In a data conversion device, a plurality of series of data to be converted is input from a buffer memory device to a data processor. The data processor processes a plurality of the series of the data to be converted, simultaneously in parallel, and outputs a plurality of the series of the data to be converted, simultaneously in parallel. A memory controller of the buffer memory device relates a plurality of the series of the data to be converted to respective conversion tables formed therein by the data processor so as to read converted data corresponding to the series of the data to be converted from the respective conversion tables simultaneously in parallel.