An apparatus for decoding an image, the apparatus comprising: a processor which is configured for determining plurality of square maximum coding units from an image and determining a square coding unit which is hierarchically split from a maximum coding unit among the plurality of maximum coding units using information about a coding unit, wherein the information about a coding unit is parsed from the bitstream; and a decoder which is configured for reconstructing residuals by performing inverse quantization and inverse transformation on quantized transformation coefficients of a transformation unit parsed from the bitstream, performing intra prediction or inter prediction using at least one prediction unit included in the coding unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein the processor is configured for determining the at least one prediction unit, which is split from the coding unit using information about a prediction unit, wherein the information about a prediction unit is parsed from the bitstream, and determining at least one transformation unit, which is split from the coding unit using information about a transformation unit, wherein the information about a transformation unit is parsed from the bitstream, wherein when a prediction mode is determined to be an inter prediction mode and not an intra prediction mode, the apparatus for decoding is configured to support a transformation unit, among the at least one transformation unit, having a size of 2N x 2N, that includes four prediction units, among the at least one prediction unit, having a size of N x N, wherein the at least one prediction unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing at least one of height and width of the coding unit, and wherein the transformation unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing height and width of the coding unit. a processor which is configured for determining plurality of square maximum coding units from an image and determining a square coding unit which is hierarchically split from a maximum coding unit among the plurality of maximum coding units using information about a coding unit, wherein the information about a coding unit is parsed from the bitstream; and a decoder which is configured for reconstructing residuals by performing inverse quantization and inverse transformation on quantized transformation coefficients of a transformation unit parsed from the bitstream, performing intra prediction or inter prediction using at least one prediction unit included in the coding unit to generate a predictor, and reconstructing the coding unit using the residuals and the predictor, wherein the processor is configured for determining the at least one prediction unit, which is split from the coding unit using information about a prediction unit, wherein the information about a prediction unit is parsed from the bitstream, and determining at least one transformation unit, which is split from the coding unit using information about a transformation unit, wherein the information about a transformation unit is parsed from the bitstream, wherein when a prediction mode is determined to be an inter prediction mode and not an intra prediction mode, the apparatus for decoding is configured to support a transformation unit, among the at least one transformation unit, having a size of 2N x 2N, that includes four prediction units, among the at least one prediction unit, having a size of N x N, wherein the at least one prediction unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing at least one of height and width of the coding unit, and wherein the transformation unit is one among blocks including: a block equal in size to the coding unit; and a block among a plurality of blocks generated by equally dividing height and width of the coding unit.