An encoding method comprising the steps of: supplying three different parity check polynomials for creating a low-density parity-check convolutional code (LDPC-CC) matrix, the LPDC-CC having a coding rate of (n-1)/n where n is an integer of 2 or more, period 3, wherein in the parity check matrix the three polynomials are arranged repeatedly by switching the three different parity check polynomials by a period of 3 periodically and in sequential manner and generating a low-density parity-check convolutional codeword using input data and the parity check matrix, characterized in that the three different parity check polynomials are respectively represented by three check equations, and, D being a delay operator, X j, which is an information sequence X j polynomial representation where j is an integer of one or more, and n-1 or less, and P, which is a parity sequence polynomial representation; and the exponent of the coefficients of the X j and the exponent of the coefficients of the P represent values which indicate the position of the element "1" in the row of a parity check matrix, a #k,j,1, a #k,j,2, and a #k,j,3 where k=1, 2, 3, which are the exponents of the coefficient of the X j, are integers, where a #k,j,1 ≠a #k,j,2#k,j,3, b #k,1, b #k,2, and b #k,3 where k=1, 2, 3, which are the exponents of the coefficient of the P, are integers, where b# k,1 ≠b #k,2 ≠b #k,3, satisfying a remainder rule defined by the conditions of each of combinations (a #k,j,1 %3, a #k,j,2 %3, a #k,j,3 %3) where k=1, 2, 3 which is a combination of remainders obtained by dividing the exponents of the coefficient of the X j by 3, is any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0), and each of combinations (b #k,1 %3, b #k,2 %3, b #k,3 %3) where k=1, 2, 3 which is a combination of remainders obtained by dividing the exponents of the coefficient of the P by 3, is any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0), such that, when belief propagation decoding is performed, belief in each check equation is propagated to all other check equations, where the check equations are defined as: ∑ j = 1 n − 1 D a# 1, j 1 + D a# 1, j 2 + D a# 1, j 3 X j D + D b# 1, 1 + D b# 1, 2 + D b# 1, 3 P D = 0 ∑ j = 1 n − 1 D a# 2, j, 1 + D a# 2, j, 2 + D a# 2, j, 3 X j D + D b# 2, 1 + D b# 2, 2 + D b# 2, 3 P D = 0 ∑ j = 1 n − 1 D a# 3, j, 1 + D a# 3, j, 2 + D a# 3, j, 3 X j D + D b# 3, 1 + D b# 3, 2 + D b# 3, 3 P D = 0 supplying three different parity check polynomials for creating a low-density parity-check convolutional code (LDPC-CC) matrix, the LPDC-CC having a coding rate of (n-1)/n where n is an integer of 2 or more, period 3, wherein in the parity check matrix the three polynomials are arranged repeatedly by switching the three different parity check polynomials by a period of 3 periodically and in sequential manner and generating a low-density parity-check convolutional codeword using input data and the parity check matrix, the three different parity check polynomials are respectively represented by three check equations, and, D being a delay operator, X j, which is an information sequence X j polynomial representation where j is an integer of one or more, and n-1 or less, and P, which is a parity sequence polynomial representation; and the exponent of the coefficients of the X j and the exponent of the coefficients of the P represent values which indicate the position of the element "1" in the row of a parity check matrix, a #k,j,1, a #k,j,2, and a #k,j,3 where k=1, 2, 3, which are the exponents of the coefficient of the X j, are integers, where a #k,j,1 ≠a #k,j,2#k,j,3, b #k,1, b #k,2, and b #k,3 where k=1, 2, 3, which are the exponents of the coefficient of the P, are integers, where b# k,1 ≠b #k,2 ≠b #k,3, satisfying a remainder rule defined by the conditions of each of combinations (a #k,j,1 %3, a #k,j,2 %3, a #k,j,3 %3) where k=1, 2, 3 which is a combination of remainders obtained by dividing the exponents of the coefficient of the X j by 3, is any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0), and each of combinations (b #k,1 %3, b #k,2 %3, b #k,3 %3) where k=1, 2, 3 which is a combination of remainders obtained by dividing the exponents of the coefficient of the P by 3, is any of (0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), or (2, 1, 0), such that, when belief propagation decoding is performed, belief in each check equation is propagated to all other check equations, where the check equations are defined as: ∑ j = 1 n − 1 D a# 1, j 1 + D a# 1, j 2 + D a# 1, j 3 X j D + D b# 1, 1 + D b# 1, 2 + D b# 1, 3 P D = 0 ∑ j = 1 n − 1 D a# 2, j, 1 + D a# 2, j, 2 + D a# 2, j, 3 X j D + D b# 2, 1 + D b# 2, 2 + D b# 2, 3 P D = 0 ∑ j = 1 n − 1 D a# 3, j, 1 + D a# 3, j, 2 + D a# 3, j, 3 X j D + D b# 3, 1 + D b# 3, 2 + D b# 3, 3 P D = 0