A packet combining device for a communication system using hybrid automatic repeat request (HARQ) includes: a HARQ buffer; a combiner configured to combine data which is previously received and stored in the HARQ buffer with newly-received data; and a channel decoder configured to attempt channel decoding by using the combined received data provided from the combiner and provide one or more of log likelihood ratios (LLRs) computed for a systematic bit and a parity bit of the combined received data to the combiner such that the one or more LLRs are combined with the data used for channel decoding.