In response to a partial codestream truncation command, a partial codestream truncation process unit temporarily truncates a code line of encoded data. The partial codestream truncation process unit can also temporarily truncate the code line frame by frame. In response to an undo command, a restoration process unit restores the encoded data that has temporarily truncated code line. The temporarily truncated frames are included in a group of frames of the moving image. In response to an undo releasing command, a code line discarding unit discards the temporarily truncated code line or frames. The encoded data has a form of JPEG2000 or Motion-JPEG2000.