To provide a DLL creation method for an image forming device, configured to easily create appropriate dynamic link libraries for each type of devices electrically detachable from the body of the image forming device.

A DLL creation method for an image forming device includes the steps of: determining by using a computer whether a function corresponding to a device-based DLL, which is a dynamic link library prepared for each type of devices electrically detachable from the body of the image forming device, is included in function specifications which is a document describing functions of the image forming device, on the basis of a predetermined keyword in the function specifications (S135); generating a configuration switch by using a source file of the device-based DLL determined by the computer that the corresponding function is included in the function specifications, as a file to be compiled (s136); and compiling the file specified by the configuration switch to create the device-based DLL.