A data processing apparatus improves speed and efficiency of transfer of bit data, especially, multivalue data bit plane. For this purpose, a memory 50 holds four 8-bit multivalue data per 1 word, and bit plane coding processing is made by 44 (=16) multivalue data (processing block). In a memory area 51, the most significant bit (bit 7) of respective multivalue data (data 0 to 15 in FIG. 5) is collected in the order of multivalue data, and stored in one position (hatched portions in FIG. 5). Similarly, bit 6 is collected from the respective multivalue data and stored in one position.