PURPOSE:To attain the synthesization of images of high quality by cutting a hard key graphic showing the area occupied by an object with a conical curved surface whose radius changes by the rotational angle for production of a soft key graphic, therefore eliminating the undesired swelling of a key area, attaining the change of soft quantity according to the places to eliminate the overs and shorts of soft quantity in each place, and furthermore dealing with even the moving blur of the object to be extracted. CONSTITUTION:An edge detecting part 2 and a motion vector detecting part 4 calculate the edge intensity and a motion vector on a hard key boundary line based on the inputted hard key signal and then produce a transformational parameter. A curved surface generating part 5 deforms a reference curved surface based on the transformational parameter to produce a transformational curved surface. At the same time, a soft key generating part 6 cuts the boundary line part of a hard key graphic corresponding to the hard key signal based on the transformational curved surface to produce a soft key graphic.