PURPOSE: To reduce the circuit scale by using a video signal interpolated for motion compensation so as to detect a motion vector with a half picture element accuracy thereby reducing the memory capacity and the number of interpolation circuits.

CONSTITUTION: An input video signal from an input terminal 1 is given to a delay circuit 2 and to a motion vector detection circuit 5 via frame memories 3, 4. The output of the memories 3, 4 and a video signal of a current frame from the terminal 1 are given to a matching arithmetic operation circuit 31 of the circuit 5, a reference block and a retrieval block are calculated to obtain a motion vector of accuracy of 1 picture element. The address of the frame memories 15, 16 is controlled. On the other hand, the output of the circuit 2 is given to a switch circuit 6 and to arithmetic circuits 26, 27 of the motion compensation circuit 7. Picture element data are read from the memories 15, 16 based on a motion vector of the circuit 5 to obtain a motion vector of the accuracy of 1/2 picture element by the circuits 26, 27 via interpolation circuits 22, 23 to control the address of the memories 24, 25 thereby forming prediction blocks in the forward and backward directions.