Disclosed herein is a video decoding method including: obtaining a transform skip mode flag indicating whether or not a transform skip mode is applied to a current block; based on the transform skip mode flag, when a transform skip mode is applied to the current block, determining that secondary transform/inverse transform is not applied to the current block; and, according to the transform skip mode flag, when a transform skip mode is not applied to the current block, obtaining a transform matrix index for secondary transform/inverse transform of the current block and, according to the transform matrix index, determining whether or not secondary transform/inverse transform is applied to the current block.