1. A video decoding apparatus comprising: a receiver which obtains, from a bitstream, a split transformation flag indicating whether a transformation unit included in a coding unit is split, and determines a size of the transformation unit based on the split transformation flag; a context modeler which determines a context model based on the size of the transformation unit and a color component of a picture including the transformation unit; and an entropy decoder which obtains a transformation coefficient flag indicating whether at least one non-zero coefficient is included in a block of the transformation unit by entropy-decoding the bitsteam based on the context model, and obtains a transformation coefficient included in the transformation unit based on the transformation coefficient flag.