A radio communication apparatus, a radio communication method, and a radio communication system, which are capable of improving receiving reliability of predetermined bits such as bits having a high degree of importance, and the like, are provided. A code length L is decided based on the modulation system and the coding rate being specified, and the bit length of S2. The relay station decides a coding rate of S1 from the code length L. In the case of 16 QAM, since a half of all bits correspond to the bits used as the object of the quadrant discrimination, the bit length of S1 is set to L/2. Therefore, the coding rate of S1 is 2(LS1)/L, where the bit length of S1 is LS1. In the present example, S1 is coded and gives S1+P1, and S2 is coded and gives S2+P4. P1 denotes the parity bit of S1, and P4 denotes the parity bit of S2. The relay station changes the bit arrangement such that all bits of the code word (S1+P1) of S1 come to the position of the quadrant discrimination in the constellation of 16 QAM respectively.