On input coded data, variable length decoding is performed, and motion vector information extracted. The motion vector information is transmitted to the threshold value determination section, and a predetermined threshold value and the value of the motion vector information are compared. Based on the number of motion vector information whose values are the threshold value or more, it determines whether it is necessary to control the interframe motion or not. When the control is necessary because the interframe motion is large, the control signal generation section generates a control signal to suspend the decoding by the varibale length decoding section and thereby reducing a frame rate.