A data processing apparatus includes a ROM (Read Only Memory) having a validity verification program stored therein, an auxiliary storage device including a plurality of storage areas having a plurality of target verification data stored therein, an execution unit configured to perform a validity verification process on the plural target verification data in accordance with the validity verification program. An order of priority is assigned to the plural target verification data. The plural storage areas have addresses that is recognizable by the execution unit. The execution unit is configured to determine validity of each of the plural target verification data based on the order of priority until one of the plural target verification data is determined to be valid.