1. An arithmetic decoding device that decodes coded data for each of unit regions of a target image, comprising: context index deriving circuitry configured to: (a) derive at least one context index of at least one transform coefficient presence/absence flags indicating whether a transform coefficient is 0 in the each of the unit regions, the at least one transform coefficient presence/absence flag including at least one of a transform coefficient presence/absence flags related to luminance and a transform coefficient presence/absence flags related to chrominance; and (b) set (i) a first common context index for the transform coefficient presence/absence flag that is related to luminance and belongs to a DC coefficient of each of the unit regions, the first common context index being common to at least two unit regions having different sizes among the unit regions and (ii) a second common context index for the transform coefficient presence/absence flag that is related to chrominance and belongs to a DC coefficient of each of the unit regions, the second common context index being common to the at least two unit regions having different sizes among the unit regions; and syntax decoding circuitry configured to perform arithmetic decoding of the at least one transform coefficient presence/absence flag based on at least one of a probability state designated by the first common context index and a probability state designated by the second common context index.