A data processing apparatus includes an arithmetic circuit and a peripheral device protection circuit that controls access of the arithmetic circuit to the peripheral devices. The peripheral device protection circuit has a first protection preset value and a second protection preset value set as a protection level higher than that of the first protection preset value. The peripheral device protection circuit includes: a setting selection circuit that generates access permission/denial information by referring to the first protection preset value and the second protection preset value when the arithmetic circuit operates at a first operation authority level, or by referring to the second protection preset value when the arithmetic circuit operates at the second operation authority level. An access protection circuit that determines permission/denial of access to the peripheral devices based on access information output from the arithmetic circuit and the access permission/denial information.