Provided is an image decoding method performed by a decoding apparatus, which includes: decoding a first coding tree unit (CTU) in a current picture; storing motion information of the first CTU in a line buffer; and decoding a second CTU in the current picture by using the motion information of the first CTU stored in the line buffer, in which the first CTU is located around a left side of the second CTU or located around a top of the second CTU.