An encoding apparatus encoding a bitstream including an image frame is disclosed. The encoding apparatus comprises a selection unit for selecting a plurality of pixels including non-zero transform coefficients in a transform coefficient block constituting an image frame, an inverse transform unit for generating a plurality of groups of code candidates including combinations of codes assignable to the non-zero transform coefficients of the selected plurality of pixels and generating candidate reconstruction blocks by performing an inverse transform on each of the transform coefficient blocks in which the sign is assigned to the non-zero transform coefficients according to the generated plurality of groups of code candidates, a cost calculation unit for calculating a cost on the basis of a pixel value difference between pixel values of a plurality of pixels selected from among the generated candidate reconstruction blocks and pixel values of other pixels adjacent to the selected plurality of pixels and an encoding unit for assigning different predetermined codewords to a plurality of groups of code candidates on the basis of the calculated cost and encoding one codeword of the codewords into encoding information of non-zero transform coefficients of the selected plurality of pixels.