An inter prediction method performed by a decoding apparatus, the method comprising: obtaining picture order count information of reference pictures, which are used for inter prediction of a current picture and are prior to the current picture in a decoding order, from a bitstream; deriving picture order count values for specifying the reference pictures based on the picture order count information; constructing a reference picture set based on the derived picture order count values of the reference pictures of the current picture; constructing a reference picture list based on the reference picture set; and performing the inter prediction on a current block based on the reference picture list to derive a predicted sample of the current block, characterized in that a picture order count value for specifying an i-th reference picture in the reference picture set is derived based on a picture order count difference specified by the picture order count information, wherein the picture order count information is included in a slice header, wherein the picture order count difference specifies a difference between picture order count values of the current picture and the i-th reference picture when the i-th reference picture is a first reference picture firstly specified by the picture order count information in the reference picture set, and wherein the picture order count difference specifies a difference between picture order count values of the i-th reference picture and an (i-1)-th reference picture when the i th reference picture is a subsequent reference picture subsequent to the first reference picture specified by the picture order count information in the reference picture set. obtaining picture order count information of reference pictures, which are used for inter prediction of a current picture and are prior to the current picture in a decoding order, from a bitstream; deriving picture order count values for specifying the reference pictures based on the picture order count information; constructing a reference picture set based on the derived picture order count values of the reference pictures of the current picture; constructing a reference picture list based on the reference picture set; and performing the inter prediction on a current block based on the reference picture list to derive a predicted sample of the current block, characterized in that a picture order count value for specifying an i-th reference picture in the reference picture set is derived based on a picture order count difference specified by the picture order count information, wherein the picture order count information is included in a slice header, wherein the picture order count difference specifies a difference between picture order count values of the current picture and the i-th reference picture when the i-th reference picture is a first reference picture firstly specified by the picture order count information in the reference picture set, and wherein the picture order count difference specifies a difference between picture order count values of the i-th reference picture and an (i-1)-th reference picture when the i th reference picture is a subsequent reference picture subsequent to the first reference picture specified by the picture order count information in the reference picture set.