In a microprocessor that internally has a microprocessor specific secret key, a key management unit is provided to carry out a key registration for reading out from an external memory a distribution key that is obtained in advance by encrypting the instruction key by using a public key corresponding to the secret key, decrypting the distribution key by using the secret key to obtain the instruction key, and registering the instruction key in correspondence to a specific program identifier for identifying the program into a key table, and to notify a completion of the key registration to the processor core asynchronously by interruption when the key registration is completed.