Abstract: A block boundary where blocking artifact occurs or a lock where ringing artifact occurs is definitely detected. The noise detecting method includes the steps of: extracting coding information, including orthogonal transformation coefficients and a motion vector of each of multiple blocks of an image, from a bitstream that has been encoded through motion compensation of the image, orthogonal transformation and quantization, where the orthogonal transformation is performed on each said block; obtaining a reference area of each said block from a reference frame using the motion vector of the block; and detecting coding noise to be eliminated according to frequency component distributions of the orthogonal transformation coefficients of each said block and another one of the blocks within the reference frame overlapping the reference area of the block.