PURPOSE: To shorten install time required for operating a device and to prevent the workability of the device from being lowered by setting levels to the files of install and preferentially executing the install of the file to be immediately required.

CONSTITUTION: A file A at a level (a) with the less margin of install timing, namely, a file with high immediateness such as a file at a level with margin by installing the file of programs or data at certain level required for operating the device or the file of programs or data for processing a maintenance check, for example, is installed by utilizing the idle time of the device. Even when the contents of the file are changed in this case, the time for installing the file for operating the device is shortened and as a result, the waiting time of install to be executed in the biginning of the device operation can be shortened. Thus, the workability of the device can be improved.