A data processing apparatus includes a memory, a processor which outputs write data when making a write request to the memory, and which inputs read data when making a read request to the memory, a first circuit which is coupled between the memory and the processor, and which includes a parity generating circuit generating a parity comprising a plurality of parity bits from the write data, the parity being written with the write data into the memory, and a second circuit which is coupled between the memory and the processor, and which includes a parity check circuit detecting a presence or an absence of an error of one-bit or two-bits in the read data and the parity read from the memory.