Disclosed is a method for transmitting data comprised of bits with higher priority and bits with lower priority output from a coder, using a high-order modulator in which a bit stream comprised of at least 3 bits represents one symbol and includes a first bit part with higher reliability and a second bit part with lower reliability. The method comprises modulating the bits with higher priority and the bits with lower priority such that the bits with higher priority are mapped to the first bit part and the bits with lower priority are also mapped to the first bit part at initial transmission; and modulating the bits with higher priority and the bits with lower priority such that the bits with higher priority are mapped to the second bit part and the bits with lower priority are mapped to the first bit part at retransmission.