A transmission processing method comprising: an encoding step of encoding information bits into a codeword according to a low density parity check code with code rate 7/15 and a codeword length of 16200, the low density parity check code shown in Table 1-1: a parity-interleaving step of conducting parity interleaving on bits of the codeword obtained in the encoding step; a column-row-interleaving step of conducting column-row interleaving on bits of the parity interleaved codeword obtained in the parity-interleaving step, the column-row interleaving being conducted with or without twist; a bit-to-cell demultiplexing step of demultiplexing a sequence of bits column-row interleaved in the column-row interleaving step into 8 sequences of bits v i,j, wherein i denotes one of the eight sequences and bit v i,j corresponds to bit v i+8×j of said sequence of column-row interleaved bits and performing a permutation on the 8 sequences of bits according to a predetermined permutation rule so as to permute each set of 8 bits (v 0,q, v 1,q, v 2,q, v 3,q, v 4,q, v 5,q, v 6,q, v 7,q) to a set of 8 bits (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) to obtain 8 sequences of permuted bits, where q is an index; a mapping step of mapping each of 8-bit cell words (y 0,q, y 1,q, y 2,q, y 3,q, y 4,q, y 5,q, y 6,q, y 7,q) each composed of a set of 8 bits (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) of the 8 sequences of permuted bits obtained in the bit-to-cell demultiplexing step, into a complex cell (Re(Zq), Im(Zq)) according to the 256QAM, Quadrature Amplitude Modulation, constellation shown in Tables 1-2 and 1-3: [Table 1-2] y 0,q 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 y 2,q 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 y 4,q 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 y 6,q 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 Re( z q) -15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 [Table 1-3] y 1,q 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 y 3,q 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 y 5,q 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 y 7,q 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 Im( z q) -15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 wherein (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) = (y 0,q, y 1,q, y 2,q, y 3,q, y 4,q, y 5,q, y 6,q, y 7,q), the predetermined permutation rule is: v 0,q = b 2,q, v 1,q = b 6,q, v 2,q = b 0,q, v 3,q = b 1,q, v 4,q = b 4,q, v 5,q = b 5,q, v 6,q = b 3,q, v 7,q = b 7,q, and the column-row interleaving of the column-row-interleaving step is performed using an interleaver matrix having a size of 2025 rows and 8 columns. an encoding step of encoding information bits into a codeword according to a low density parity check code with code rate 7/15 and a codeword length of 16200, the low density parity check code shown in Table 1-1: a parity-interleaving step of conducting parity interleaving on bits of the codeword obtained in the encoding step; a column-row-interleaving step of conducting column-row interleaving on bits of the parity interleaved codeword obtained in the parity-interleaving step, the column-row interleaving being conducted with or without twist; a bit-to-cell demultiplexing step of demultiplexing a sequence of bits column-row interleaved in the column-row interleaving step into 8 sequences of bits v i,j, wherein i denotes one of the eight sequences and bit v i,j corresponds to bit v i+8×j of said sequence of column-row interleaved bits and performing a permutation on the 8 sequences of bits according to a predetermined permutation rule so as to permute each set of 8 bits (v 0,q, v 1,q, v 2,q, v 3,q, v 4,q, v 5,q, v 6,q, v 7,q) to a set of 8 bits (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) to obtain 8 sequences of permuted bits, where q is an index; a mapping step of mapping each of 8-bit cell words (y 0,q, y 1,q, y 2,q, y 3,q, y 4,q, y 5,q, y 6,q, y 7,q) each composed of a set of 8 bits (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) of the 8 sequences of permuted bits obtained in the bit-to-cell demultiplexing step, into a complex cell (Re(Zq), Im(Zq)) according to the 256QAM, Quadrature Amplitude Modulation, constellation shown in Tables 1-2 and 1-3: [Table 1-2] y 0,q 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 y 2,q 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 y 4,q 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 y 6,q 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 Re( z q) -15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 [Table 1-3] y 1,q 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 y 3,q 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 y 5,q 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 y 7,q 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 Im( z q) -15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 wherein (b 0,q, b 1,q, b 2,q, b 3,q, b 4,q, b 5,q, b 6,q, b 7,q) = (y 0,q, y 1,q, y 2,q, y 3,q, y 4,q, y 5,q, y 6,q, y 7,q), the predetermined permutation rule is: v 0,q = b 2,q, v 1,q = b 6,q, v 2,q = b 0,q, v 3,q = b 1,q, v 4,q = b 4,q, v 5,q = b 5,q, v 6,q = b 3,q, v 7,q = b 7,q, and the column-row interleaving of the column-row-interleaving step is performed using an interleaver matrix having a size of 2025 rows and 8 columns.