1. A method performed by a video encoding or decoding apparatus for intra-predicting a current block in a video image by dividing the current block into a plurality of subblocks, the method comprising: determining an intra prediction mode of the current block among a plurality of intra prediction modes, wherein the determined intra prediction mode of the current block is applied to all of the subblocks in the current block and thereby intra prediction modes of respective subblocks in the current block are not included in a bitstream, and each of the subblocks has a plurality of pixels; and sequentially reconstructing all of the subblocks in the current block by predicting a subblock, to be reconstructed among the subblocks in the current block, from at least one neighboring subblock which has already reconstructed among the subblocks in the current block using an intra prediction mode identical to the determined intra prediction mode of the current block, wherein each subblock in the current block is reconstructed by: predicting the subblock to be reconstructed in the current block, based on the determined intra prediction mode of the current block, generating a residual subblock corresponding to the subblock to be reconstructed, and generating a reconstructed subblock by adding the predicted subblock to the residual subblock, wherein the subblock to be reconstructed in the current block is predicted using one or more neighboring pixels which are selected from pixels of the at least one neighboring subblock already reconstructed in the current block, wherein the one or more neighboring pixels are selected from the pixels of the at least one neighboring subblock using the intra prediction mode identical to the determined intra prediction mode of the current block.