An apparatus of determining a context model for entropy decoding of a transformation coefficient level, the apparatus comprising: mapping unit configured to split a transformation unit into subsets having a predetermined size; context set obtaining unit configured to obtain a context set index used in entropy decoding of a first critical value flag indicating whether a significant transformation coefficient contained in a current subset has a value greater than a first critical value; context offset obtaining unit configured to obtain a context offset used in entropy decoding of the first critical value flag for a current significant coefficient based on the number of previous transformation coefficients having consecutive 1s included in a current subset when the current significant coefficient is not initially entropy-decoded in the current subset and the previous transformation coefficients having consecutive 1s are decoded before the current significant coefficient, according to a scan order of the current subset; and context determining unit configured to obtain a context index indicating a context used in entropy decoding of the first critical value flag by using the context set index and the context offset, wherein the context set obtaining unit is configured to obtain a context set index used in entropy decoding of a second critical value flag indicating whether the significant transformation coefficient has a value greater than a second critical value based on the context set index used in entropy decoding of the first critical value flag, wherein, when a color component of the transformation unit is a luminance component, the context set index of the first critical value flag is obtained based on location information of the current subset indicating at which location the current subset is located in the transformation unit, wherein, when the color component of the transformation unit is a chrominance component, the context set index of the first critical value flag is obtained independently of the location information of the current subset, wherein, the context set index of the first critical value flag is obtained further based on whether there is a significant coefficient having a value greater than 1 in a previously processed subset. mapping unit configured to split a transformation unit into subsets having a predetermined size; context set obtaining unit configured to obtain a context set index used in entropy decoding of a first critical value flag indicating whether a significant transformation coefficient contained in a current subset has a value greater than a first critical value; context offset obtaining unit configured to obtain a context offset used in entropy decoding of the first critical value flag for a current significant coefficient based on the number of previous transformation coefficients having consecutive 1s included in a current subset when the current significant coefficient is not initially entropy-decoded in the current subset and the previous transformation coefficients having consecutive 1s are decoded before the current significant coefficient, according to a scan order of the current subset; and context determining unit configured to obtain a context index indicating a context used in entropy decoding of the first critical value flag by using the context set index and the context offset, wherein the context set obtaining unit is configured to obtain a context set index used in entropy decoding of a second critical value flag indicating whether the significant transformation coefficient has a value greater than a second critical value based on the context set index used in entropy decoding of the first critical value flag, wherein, when a color component of the transformation unit is a luminance component, the context set index of the first critical value flag is obtained based on location information of the current subset indicating at which location the current subset is located in the transformation unit, wherein, when the color component of the transformation unit is a chrominance component, the context set index of the first critical value flag is obtained independently of the location information of the current subset, wherein, the context set index of the first critical value flag is obtained further based on whether there is a significant coefficient having a value greater than 1 in a previously processed subset.