PURPOSE: To make the DC component in the PCM digital signal approximate to zero as much as possible by allotting the digital signal featuring the zero DSV (digital sum variation) to the analog signal featuring a high occurring frequency quantization levels and thus changing the analog signal into PCM.

CONSTITUTION: In case the analog signal such as the video signal or the like is converted into the 8-bit code, the quantization level of the analog signal and its occurring frequency are as shown by the curve in the diagram. And in the DSV of the 8-bit code, i.e., in the binary data series, the value obtained through the cumulative sum with weighting of "0" and "1" to -1 and +1 respectively becomes 0, ±2, ±4, ±6 and ±8 each. And the smaller the value the smaller the DC component. In this connection, the digital signal of a small (large) DSV value is allotted to the analog signal featuring of the quantization level featuring a high (low) occurring frequency as shown in the diagram, thus performing the A/D conversion to attain the purpose mentioned above.