1. An encoding circuit comprising: a taking-over unit which takes over probability tables of divided regions of a previous frame image of a frame image having N divided regions continuously given at predetermined intervals to divided regions of a present frame image, respectively; an acquiring unit which acquires a parameter of an adjacent macro block of the previous frame image in calculation of a parameter of a macro block serving as a processing unit in the divided region when the macro block is located on a boundary between the divided regions; a selecting unit which calculates the acquired parameter of the adjacent macro block to select one of probability models in the probability table; and an encoding unit which arithmetically encodes a residual signal in the frame image on the basis of the selected probability model to generate an encoded bit string.