1. An encoding method comprising:

generating, by performing encoding of coding rate 2/4 on an information sequence X1 and an information sequence X2, an encoded sequence composed of the information sequence X1, the information sequence X2, and a parity sequence P, the encoding based on a predetermined parity check matrix having m×z rows and 2×m×z columns, where

m is an even number no smaller than two and z is a natural number,

wherein the predetermined parity check matrix is one of a first parity check matrix and a second parity check matrix, the

first parity check matrix corresponding to a low density parity check (LDPC) convolutional code that uses a plurality of parity

check polynomials, the second parity check matrix being generated by performing at least one of row permutation and column

permutation on the first parity check matrix,

wherein two parity check polynomials satisfying zero are provided for each of 1×P1(D) and 1×P2(D) in accordance with the LDPC convolutional code,

wherein each parity check polynomial satisfying zero of the LDPC convolutional code is expressed by one of a first group of

expressions or one of a second group of expressions,

wherein the first group of expressions consist of the following expressions:

where

p is an integer no smaller than one and no greater than two,

q is an integer no smaller than one and no greater than r#(2i),p,

when r#(2i),p is a natural number, Xp(D) is a polynomial expression of the information sequence Xp and P(D) is a polynomial expression of the parity sequence P, D being a delay operator,

?#(2i),p,q and ?#(2i),0 are natural numbers,

?#(2i),1 is a natural number,

?#(2i),2 is an integer no smaller than zero,

?#(2i),3 is a natural number,

R#(2i),p is a natural number,

1?R#(2i),p

?#(2i),p,y??#(2i),p,z holds true for ?(y, z) where y is an integer no smaller than one and no greater than r#(2i),p, z is an integer no smaller than one and no greater than r#2i,p, and y and z satisfy y?z, and

wherein the second group of expressions consist of the following expressions:

where

p is an integer no smaller than one and no greater than two,

q is an integer no smaller than one and no greater than r#(2i+1),p,

when r#(2i+1),p is a natural number, Xp(D) is a polynomial expression of the information sequence Xp and P(D) is a polynomial expression of the parity sequence P, D being a delay operator,

?#(2i+1),p,q and ?#(2i+1),0 are natural numbers,

?#(2i+1),1 is a natural number,

?#(2i+1),2 is an integer no smaller than zero,

?#(2i+1),3 is a natural number,

R#(2i+1),p is a natural number,

1?R#(2i+1),p

?#(2i+1),p,y??#(2i+1),p,z holds true for ?(y, z) where y is an integer no smaller than one and no greater than r#(2i+1),p, z is an integer no smaller than one and no greater than r(#2i+1),p, and y and z satisfy y?z.