An apparatus of decoding video, the apparatus comprising: a parser which obtains, from a bitstream, a split transformation flag for a current depth, and when the split transformation flag indicates non-split for the current depth, determines a transformation depth is equal to the current depth; a context modeler which determines a context increasement parameter for determining a context index based on only whether the transformation depth is equal to zero, and obtains a context model for arithmetic decoding a transformation unit significant coefficient flag of a luma component indicating whether a non-zero transformation coefficient exists in the transformation unit of the luma component using the context index obtained by adding the context increasement parameter and a context offset; and an arithmetic decoder which arithmetic decodes the transformation unit significant coefficient flag based on the context model, and determines whether at least one non-zero transformation coefficient exists in the transformation unit of the transformation depth, based on the transformation unit significant coefficient flag, wherein, when the transformation depth is equal to zero, the context modeler determines the context increasement parameter as one; and when the transformation depth is not equal to zero, the context modeler determines the context increasement parameter as zero, wherein, when the split transformation flag indicates a split for the current depth, a transformation unit of the current depth is split into one or more transformation units of a next depth, and a split transformation flag for the next depth is obtained from the bitstream. a parser which obtains, from a bitstream, a split transformation flag for a current depth, and when the split transformation flag indicates non-split for the current depth, determines a transformation depth is equal to the current depth; a context modeler which determines a context increasement parameter for determining a context index based on only whether the transformation depth is equal to zero, and obtains a context model for arithmetic decoding a transformation unit significant coefficient flag of a luma component indicating whether a non-zero transformation coefficient exists in the transformation unit of the luma component using the context index obtained by adding the context increasement parameter and a context offset; and an arithmetic decoder which arithmetic decodes the transformation unit significant coefficient flag based on the context model, and determines whether at least one non-zero transformation coefficient exists in the transformation unit of the transformation depth, based on the transformation unit significant coefficient flag, wherein, when the transformation depth is equal to zero, the context modeler determines the context increasement parameter as one; and when the transformation depth is not equal to zero, the context modeler determines the context increasement parameter as zero, wherein, when the split transformation flag indicates a split for the current depth, a transformation unit of the current depth is split into one or more transformation units of a next depth, and a split transformation flag for the next depth is obtained from the bitstream.