PURPOSE: To suppress picture quality fluctuation of a reproduced picture attended with information quantity control.

CONSTITUTION: Coded original picture data are stored in a buffer memory 6 and sent at a prescribed speed. A generated information quantity storage circuit 22 stores a past generated information quantity in the unit of transmission and an allocation correction circuit 21 changes an allocation ratio in the unit of transmission accordingly. A quantization parameter control circuit 20 utilizes the determined allocation quantity to set a quantization parameter so as to let a generated information quantity be optimum thereby making a step width at the time of quantization suitable thereto. Thus, the fluctuation of the step width in the unit of transmission is suppressed and fluctuation of picture quality of a reproduced picture is not remarkable.