A programmable controller controls operations of a control target connected thereto by periodically and repeatedly performing sequence programs thereby performing a predetermined process. The sequence programs are stored in a user program storage unit in the programmable controller, and are loaded on a memory in the programmable controller to be executed by an MPU (Micro Processing Unit). The sequence programs may break due to accidental problems. Methods of backing up the sequence programs have been conventionally proposed for preventing breaking of the sequence programs. For example, a conventional technology has been known in which the sequence programs are stored by executing a write command on a management computer or a storage medium, such as a memory, connected to the programmable controller via a communication interface.
The programmable controller is of course used by a user (hereinafter, referred to as an end user); however, normally, a system designer (hereinafter, referred to as a set maker) constructs a system including sequence programs or control parameters that meets the desire of the end user by using the programmable controller manufactured by a manufacturer (hereinafter, referred to as a maker). These sequence programs, or the parameters for operating the constructed system include technical know-how and the like that the set maker would like to keep confidential. Therefore, set makers want to keep the sequence programs or the parameters confidential to prevent unauthorized copying or the like of the sequence programs or the parameters.
Therefore, a technology has been proposed in which unique information of each device for identifying a programmable controller or for protecting each setting information is embedded when sequence programs are saved on a storage medium, a protection key for preventing unauthorized copying is compared with the unique information of each device when the sequence programs are read from the storage medium to the programmable controller, and readout of the sequence programs is allowed only when the unique information matches the protection key (e.g., see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-open No. 2006-106998