A decoding device that decodes a coded picture signal (Str) comprising a header stream (Str_H) and a frame stream (Str_F), the header stream (Str_H) including header information which is common information of a whole picture signal corresponding to slice data comprising a plurality of macroblocks, and the frame stream (Str_F) including frame information which is the picture signal itself corresponding to the slice data comprising the plurality of macroblocks, said decoding device comprising: a demultiplexer configured to receive the coded picture signal (Str) and to demultiplex the coded picture signal (Str) into the header stream (Str_H) and the frame stream (Str_F); a header stream decoding unit (25, 26, 41, 42, 43) configured to receive the header stream (Str_H) and to perform a decoding process on the header information selectively using a fixed length decoding method and a variable length decoding method; and a frame information decoding unit (44, 27) configured to receive the frame stream (Str_F) and to perform a decoding process on the frame information using an arithmetic decoding method as a single decoding method so as to output all decoded macroblocks of the slice data, wherein the header stream decoding unit (25, 26, 41, 42, 43) includes a selecting unit configured to select one of a fixed length decoding method or a variable length decoding method according to a syntax structure signal (Stx_H), and wherein the header stream decoding unit (25, 26, 41, 42, 43) is configured to decode the header information corresponding to a fixed length code, using one of a plurality of fixed length decoding methods according to the syntax structure signal (Stx_H), when the fixed length decoding method is selected by the selecting unit, and the header stream decoding unit is configured to decode the header information corresponding to a variable length code, using one of a plurality of variable length decoding methods according to the syntax structure signal (Stx_H), when the variable length decoding method is selected by the selecting unit. a demultiplexer configured to receive the coded picture signal (Str) and to demultiplex the coded picture signal (Str) into the header stream (Str_H) and the frame stream (Str_F); a header stream decoding unit (25, 26, 41, 42, 43) configured to receive the header stream (Str_H) and to perform a decoding process on the header information selectively using a fixed length decoding method and a variable length decoding method; and a frame information decoding unit (44, 27) configured to receive the frame stream (Str_F) and to perform a decoding process on the frame information using an arithmetic decoding method as a single decoding method so as to output all decoded macroblocks of the slice data, wherein the header stream decoding unit (25, 26, 41, 42, 43) includes a selecting unit configured to select one of a fixed length decoding method or a variable length decoding method according to a syntax structure signal (Stx_H), and wherein the header stream decoding unit (25, 26, 41, 42, 43) is configured to decode the header information corresponding to a fixed length code, using one of a plurality of fixed length decoding methods according to the syntax structure signal (Stx_H), when the fixed length decoding method is selected by the selecting unit, and the header stream decoding unit is configured to decode the header information corresponding to a variable length code, using one of a plurality of variable length decoding methods according to the syntax structure signal (Stx_H), when the variable length decoding method is selected by the selecting unit.