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) read the one or more program instructions of the first set of program instructions from the storing unit and store the one or more read program instructions in a protected memory, the protected memory being protected such that an external device is unable to observe content of the memory, (ii) 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 the protected memory, and (iii) execute, when judging negatively, one or more program instructions of the second set of program instructions.