A programmable controller system is formed by connecting a personal computer having an aid device program module installed to serve as an aid device for development of control program to a programmable controller having password protect function. A hardware key storing a specified password code is detachably attached to the personal computer. The aid device program module checks whether or not software module with a function of certifying a hardware key exists and if it is found to exist, it is linked as a part of the aid device program module and the function of certifying the hardware key is caused to operate.