A method by which a first wireless apparatus transmits a signal on the basis of a hybrid automatic repeat request (HARQ) by using a parity check (PC) polar code in a wireless communication system, according to one embodiment of the present specification, comprises the steps of: generating a first codeword on the basis of a first PC polar code; transmitting the first codeword; generating a second codeword on the basis of a second PC polar code; and transmitting the second codeword.