The present invention includes methods and apparatus for attaining high speed coding and decoding. A first method decreases the number of memory access times by performing signal format conversion, orthogonal transform and continuous variable-length coding with predetermined small areas in a frame used as units. A second method omits orthogonal transform computation by using orthogonal transform coefficients to shorten the processing time. A third method uses additions and subtractions for orthogonal transform thereby decreasing the number of registers used and reducing the number of memory access times. The present invention further includes a decoding method for variable-length decoding wherein table size is not made larger because the number of table access times per code word is set to a maximum of 2, and plural code words are decoded by one table access operation to attain high-speed decoding.