1. A program writable IC card, comprising: a microprocessor; a memory for storing a program write control program having at least one of a decryption function and a function for converting a program code and a program for said microprocessor; and means in said microprocessor for performing at least one of said decryption process and said process of converting a program code according to said program write control program and storing said program in said memory when said program for said microprocessor is given from the outside.