PURPOSE: To reduce the circuit scale without deteriorating the performance by selectively outputting a fixed length code from 1st and 2nd conversion tables depending on a bit length code.

CONSTITUTION: A 1st conversion table 2 converts a variable length code into a conversion code with a short bit length when the variable length code is made up of a bit length longer than the bit length of a high-order bit and outputs the result to a 2nd conversion table 3. The 2nd conversion table 3 receives the conversion code as a high-order bit of an address and a low-order bit of the variable length code as a low-order bit of the address and converts the preceding variable length code into a fixed length code and outputs the converted code to a selector 4. The selector 4 based on the bit length code representing the bit length pattern outputs selectively the fixed length code from the 1st and 2nd conversion tables 2 and 3. Thus, the circuit scale is reduced without deteriorating the conversion performance.