PURPOSE: To implement fixed length coding by controlling a code quantity within a prescribed quantity in the orthogonal transformation coder.

CONSTITUTION: Total activity obtained by a bit length of an AC component of a transformation code and a total code quantity of a DC component are calculated by a 1st scanning. Then actual coding is implemented in a 2nd scanning, a normalized quantization table 16 is normalized based on the said total activity and the AC component is quantized by an AC quantization section 12. Moreover, a block bit arrangement control section 21 compares a bit arrangement quantity for each block with a code quantity being an output of an AC Huffman coding section 15, a block bit arrangement control section 21 outputs a code stop instruction to the AC Huffman coding section 15 from the block bit arrangement control section 21 when the code quantity exceeds the bit arrangement quantity to stop the coding. Then a multiplexer 27 synthesizes the DC component and the AC component and outputs the result.