A data processing apparatus including a processor and a memory has a parity/ECC encoder circuit and a parity/ECC decoder circuit. The parity/ECC encoder circuit is disposed in a signal path for writing data to the memory, includes a parity generating circuit for generating a parity of a plurality of bits from data to be written, and writes the generated parity together with the data into the memory. The parity/ECC decoder circuit is disposed in a signal path for reading data from the memory and includes a parity check unit. The parity generating circuit is configured so that each of a plurality of bits configuring the data contributes to generation of a parity of at least two bits. Consequently, the parity check unit can detect a two-bit error at high speed.