A device for optimizing a data compression level when processing a Hybrid Automatic Repeat reQuest (HARQ) signal includes a combiner which receives a log likelihood ratio (LLR) signal, determines whether the LLR signal is a new or retransmitted signal, and generates a composite signal by combining the LLR signal with a related signal received and previously stored when the LLR signal is the retransmitted signal; a compression level decision unit which calculates a first compression level based on quality of a received signal, calculates a second compression level based on an available memory size, and decides a final compression level according to the first compression level and the second compression level; a compressor which compresses the LLR signal according to the final compression level; a HARQ memory which stores the compressed signal; and a decompressor which decompresses a signal read from the HARQ memory.