1. An apparatus of decoding video, the apparatus comprising: a parser which obtains, from a bitstream, a split transformation flag used to determine a transformation unit for inverse transformation process, and obtains at least one transformation unit from a coding unit based on the split transformation flag; a context modeler which obtains a context model for arithmetic decoding a transformation unit significant coefficient flag indicating whether a non-zero transformation coefficient exists in a transformation unit included in a coding unit, based on a transformation depth of the transformation unit; and an arithmetic decoder which arithmetic decodes the transformation unit significant coefficient flag based on the determined context model.