a p frame the prediction image is synthesized in 1003 utilizing positive rounding and this prediction image is stored in frame memory c on the other hand when the current frame is a p u2212 frame the prediction image is synthesized in 1004 utilizing negative rounding and this prediction image is stored in the frame memory c next in 1005 the differential image between frame memories a and c is found and stored in frame memory a here the process again returns to fig8 prior to starting the processing in 809 the input image is stored in frame memory a when the current frame is an i frame and the differential image between the input image and the prediction image is stored in frame memory a when the current frame is a p frame p or p u2212 frame in 809 dct is applied to the image stored in frame memory a and the dct coefficients calculated here are sent to the output buffer after being quantized in 810 inverse quantization is performed to the quantized dct coefficients and inverse dct is applied the image obtained by applying inverse dct is stored in frame memory b next in 811 it is checked again whether the current frame is an i frame when the current frame is not an i frame the images stored in frame memory b and c are added and the result is stored in frame memory b the coding process of a frame ends here and the image stored in frame memory b before going into 813 is the reconstructed image of this frame this image is identical with the one obtained at the decoding side in 813 it is checked whether the frame whose coding has just finished.