1. An information processing device comprising: a storing unit operable to store a first set of program instructions including one or more program instructions for detecting a tampering, and a second set of program instructions; and a control unit operable to (i) judge whether or not at least part of the second set of program instructions is tampered with, by executing the one or more program instructions of the first set of program instructions with use of a protected memory, the protected memory being protected such that an external device is unable to observe content of the memory, and (ii) execute, when judging negatively, one or more program instructions of the second set of program instructions.