PURPOSE: To uniformly control picture quality over entire one field.

CONSTITUTION: The delay amount of one frame in a line LO 1 is divided for the unit of a field, and a field memory 14 is arranged between an orthogonal transformation circuit 3 and a quantizer 4 in the line LO 1. Quantizing level information is calculated and supplied to the quantizer 4 and an inverse quantizer 9 to specify a quantizing characteristic Qi so that a variable length code formed by a code allocation part 5 during this one field period can not overflow from an output buffer memory 6, and the quantization/inverse quantization of a transformation coefficient EAT (n, n-1) is executed.