A program is simply stored in a storage unit of a programmable controller. A substrate of the programmable controller includes an interface unit to which an external device having input and output terminals is detachably attached and a first storage unit. The interface unit includes a processor circuit and connector terminals to which the input and output terminals of the external device are able to be connected. The method includes: forming a predetermined circuit by connecting the input and output terminals of the external device to the connector terminals; reading a program or data of the programmable controller from a second storage unit in which the program or data is stored and storing the read program or data in the first storage unit; and causing the processor circuit to start the step of reading and storing the program or data when the predetermined circuit has been formed.