PURPOSE: To prevent a motion vector from being erroneously detected and to reduce the amount of generated codes.

CONSTITUTION: The absolute value sum of difference between a block A of a present frame and a block A' of a preceding frame is calculated at a differentiator 3 and a cumulative adder 4, for example, and this is defined as residual. On the other hand, a weight calculator 13 or 14 respectively calculates weight W1 or W2 based on the motion vector detected in the past. Then, a computing element 5 calculates the weighted residual, for which the weight W1 and W2 is multiplied to the residual, and a vector indicating the position of the block A' to apply the minimum weighted residual from the position of the block A is defined as the motion vector at a minimum value detection circuit 6.