A communication system that performs encoding and decoding for communication, comprising: a transmitting apparatus; and a receiving apparatus, wherein the transmitting apparatus includes: a turbo encoding unit including a first encoding unit that encodes an input signal and generates a first parity bit by bit-based encoding and n (n = 1, 2, 3,...) second encoding units that encode the input signal and generate second parity bits by bit-based encoding; and a symbol mapping unit that maps an output from the turbo encoding unit to a symbol by bit-based mapping operation and modulates the output, wherein, when an m-th (m = 1, 2, 3,...) output systematic bit is a systematic bit Sm, an m-th output first parity bit is a parity bit P1m, and an m-th output second parity bit is a parity bit P(n+1)m, the symbol mapping unit maps the m-th systematic bit Sm, the m-th parity bit P1m, and the m-th parity bits P(n+1)m to a symbol of one of an I component and a Q component, and maps an (m+1)-th systematic bit Sm+1, an (m+1)-th parity bit P1(m+1), and (m+1)-th parity bits to P(n+1)(m+1) to a symbol of the other of the I component and the Q component, and the receiving apparatus includes: a demodulating unit that demodulates a transmission signal; and a turbo decoding unit that performs turbo decoding on the demodulated signal by bit-based decoding characterized in that the turbo decoding unit performs turbo decoding on each one of the n+1 sets composed of the systematic bit Sm and a parity bit Pkm, where 1 ≤ k ≤ n+1: k is each natural number from 1 to n+1, corresponding to the systematic bit Sm and mapped to the same symbol, without separating the bits of each set (23-1, 23-2). a transmitting apparatus; and a receiving apparatus, wherein the transmitting apparatus includes: a turbo encoding unit including a first encoding unit that encodes an input signal and generates a first parity bit by bit-based encoding and n (n = 1, 2, 3,...) second encoding units that encode the input signal and generate second parity bits by bit-based encoding; and a symbol mapping unit that maps an output from the turbo encoding unit to a symbol by bit-based mapping operation and modulates the output, wherein, a turbo encoding unit including a first encoding unit that encodes an input signal and generates a first parity bit by bit-based encoding and n (n = 1, 2, 3,...) second encoding units that encode the input signal and generate second parity bits by bit-based encoding; and a symbol mapping unit that maps an output from the turbo encoding unit to a symbol by bit-based mapping operation and modulates the output, wherein, when an m-th (m = 1, 2, 3,...) output systematic bit is a systematic bit Sm, an m-th output first parity bit is a parity bit P1m, and an m-th output second parity bit is a parity bit P(n+1)m, the symbol mapping unit maps the m-th systematic bit Sm, the m-th parity bit P1m, and the m-th parity bits P(n+1)m to a symbol of one of an I component and a Q component, and maps an (m+1)-th systematic bit Sm+1, an (m+1)-th parity bit P1(m+1), and (m+1)-th parity bits to P(n+1)(m+1) to a symbol of the other of the I component and the Q component, and the receiving apparatus includes: a demodulating unit that demodulates a transmission signal; and a turbo decoding unit that performs turbo decoding on the demodulated signal by bit-based decoding characterized in that the turbo decoding unit performs turbo decoding on each one of the n+1 sets composed of the systematic bit Sm and a parity bit Pkm, where 1 ≤ k ≤ n+1: k is each natural number from 1 to n+1, corresponding to the systematic bit Sm and mapped to the same symbol, without separating the bits of each set (23-1, 23-2). a demodulating unit that demodulates a transmission signal; and a turbo decoding unit that performs turbo decoding on the demodulated signal by bit-based decoding characterized in that the turbo decoding unit performs turbo decoding on each one of the n+1 sets composed of the systematic bit Sm and a parity bit Pkm, where 1 ≤ k ≤ n+1: k is each natural number from 1 to n+1, corresponding to the systematic bit Sm and mapped to the same symbol, without separating the bits of each set (23-1, 23-2).