A data processing device 10 is composed of a data storage unit 11 that stores first authentication data, second medium authentication data generated by applying a predetermined encryption to the first medium authentication data, and second device authentication data generated by applying the predetermined encryption to first device authentication data; a medium authentication data transmission unit 12 transmits the first medium authentication data; an encrypted data reception unit 13 receives first encrypted data; an authentication unit 14 authenticates an information recording medium 30 when the first encrypted data and the second medium authentication data are identical; a device authentication data reception unit 15 receives the first device authentication data; and a device authentication data transmission unit 16 transmits the second device authentication data. Mutual authentication processing can be performed without the data processing device having a unit for encrypting, and by using data each time. Developers of various types of software can perform data transfer operation checking, debugging and the like without the risk of secret information being leaked.