1. An encoding method comprising

generating an encoded sequence comprising: n?1 information sequences denoted as X1 through Xn-1; and a parity sequence denoted as P, by encoding the n?1 information sequences at a (n?1)/n coding rate according to a predetermined

parity check matrix having m×z rows and n×m×z columns, n being an integer no less than two, m being an even number no less

than two, and z being a natural number, wherein

the predetermined parity check matrix is a first parity check matrix or a second parity check matrix, the first parity check

matrix corresponding to a low-density parity check (LDPC) convolutional code using a plurality of parity check polynomials,

the second parity check matrix generated by performing at least one of row permutation and column permutation with respect

to the first parity check matrix, and

given e denoting an integer no less than zero and no greater than m×z?1, ? denoting an integer no less than one and no greater

than m×z, and i being a variable denoting an integer that is no less than zero and no greater than m?1 and satisfies i=e%m

where % denotes a modulo operator,

when e???1, an eth parity check polynomial that satisfies zero, of the LDPC convolutional code, is expressed as

where b1,i is a natural number, and

when e=??1, the eth parity check polynomial that satisfies zero, of the LDPC convolutional code, is expressed as

where, in Math. 1 and Math. 2,

p denotes an integer no less than one and no greater than n?1, q denotes an integer no less than one and no greater than rp,i, and rp,i denotes an integer no less than two,

D denotes a delay operator, Xp(D) denotes a polynomial representation of an information sequence Xp among the n?1 information sequences, and P(D) denotes a polynomial representation of the parity sequence P, and

ap,i,q denotes a natural number, and

when x and y are integers no less than one and no greater than rp,i and satisfy x?y, ap,i,x?ap,i,y holds true for all x and y,

when s=p, and vs,1 and vs,2 are odd numbers less than m, ap,i,q satisfies both as,i,1%m=vs,1 and as,i,2%m=vs,2 for all i, and

in Math. 1 and Math. 2,

a greatest common divisor of vs,1 and m is one, and a greatest common divisor of vs,2 and m is one, where s is an integer no less than one and no greater than n?1, and vs,1 and vs,2 are integers no less than one and no greater than m?1.