An application installing method according to the present invention in which an application file includes at least two application encrypting data in which the executable files are respectively encrypted using different encryption algorithms, and a license file includes at least two license encryption data in which application decryption keys for decrypting the application encryption data are encrypted using respectively different encryption algorithms. The process execution apparatus includes a calculation unit configured to execute the executable file, and a storage unit configured to store the application file and the license file. The method includes a step of decrypting the application encryption data by use of the application decryption key with the calculation unit based on the level of priority of the predesignated application encryption data stored in the storage unit, and installing the executable file corresponding to the application encryption data.