A controller reads out image data of an area frame that a user has drawn on an original and accurately extracts the area frame by removing noise from the read-out image data to divide image data of an area outside the area frame and image data of an area inside the area frame into separate stencils, according to a separation program. It is therefore possible to execute a separation process desired by the user without increasing costs and man-hours and with easy operations not making the user feel troublesome.