In an embodiment, an error correction code circuit is provided. The error correction code circuit includes an error correction code engine and data processing circuit. The error correction code engine is configured to generate a second parity signal and syndrome information by performing an operation on operation source data and a first parity signal. The data processing circuit is configured to output write data as the operation source data and output an internally generated dummy parity signal as the first parity signal during a write operation, and to output read data as the operation source data and output a read parity signal as the first parity signal during a read operation.