An error correction code (ECC) unit includes an error correction code (ECC) encoder configured to perform error correction code (ECC) encoding for each of a first data group and a second data group sharing at least one data with the first data group; and an error correction code (ECC) decoder configured to perform error correction code (ECC) decoding for each of the first data group and the second data group. The ECC decoder performs the ECC decoding for the second data group when the ECC decoding for the first data group fails, and does not perform the ECC decoding for the second data group when the ECC decoding for the first data group succeeds.