PURPOSE: To accomplish high-speed processing without enlarging the scale of the equipment by executing the comparison of the positions of the center of gravity of a registered picture and an input picture as making the center of gravity of the latter turn, and by obtaining an angular difference in rotation and an amount of parallel movement in order to execute the positioning.

CONSTITUTION: A picture data stored in an input picture memory 1 is differentiated by a spatial differentiating circuit 2 to obtain the density gradient and its direction of each picture element. Then the data is inputted to a gravity-center extracting circuit 3, and is sorted in different directions to obtain respective gravity-center coordinates. The data of the gravity-center coordinates are stored in an input-picture gravity-center storing register 4. The stored picture data is made turn by a gravity- center turning circuit 6. Along with this turning, the store coordinate data and the content in a registered-picture gravity-center storing register 5 are compared by a gravity-center-position comparative circuit 7. In the result of the comparison, the angle of turning by which the values of respective picture elements of the registered picture and the input picture are made coincident i.e. the angular difference in rotation and the amount of parallel movement are obtained and is supplied to a coordinate converting circuit 8 in order to process and output the positioned pictures with a high speed.