It is judged whether or not an exchange unit mounted in an image forming apparatus is a genuine one. If judged that a nongenuine unit is mounted there, it is judged at the next step whether not a control parameter is optimized. If judged that the control parameter is optimized, it is judged at the next step whether or not the control parameter is optimized in a local environment. If not optimized in the local environment, an optimal parameter is downloaded from a website.