A program control system is capable of preventing an invalid program from being downloaded to a mobile terminal. When a programmer applies for the certification and registration of a developed program, a gateway sends a checking program for checking the validity of program to the programmer. After having been notified that the program had passed the check from the programmer, the gateway accepts the registration of the program, and requests a cipher key database to send a public key. Having received the public key from the cipher key database, the gateway sends the program with the public key to a server to register the program. When a mobile terminal requests for the program, the gateway accesses the server to obtain the program with the public key. Subsequently, the gateway sends the public key to the cipher key database to authenticate the public key by use of a companion cipher key stored therein. The gateway downloads the program to the mobile terminal only when the public key is authenticated and thereby the program proves to be valid.