A system for preventing an unauthorized software copying prevention mechanism from being invalidated by a program falsification, includes an inherent key generator for generating an inherent key peculiar to a software user data processing device, a secret information encrypting unit for encrypting secret information indispensable for software to operate properly, which is stored by a secret information storage unit, with an inherent key, and a falsification detector for inspecting whether the system for preventing unauthorized copying of software, which is operating on the software user data processing device, has been falsified or not. If the system has not been falsified, then the inherent key generator generates the inherent key. If the system has been falsified, then a secret information destroyer destroys the encrypted secret information stored by an encrypted secret information storage unit by erasing the secret information or writing a pseudo-random number into the secret information.