A printer determines in S11 to S15 whether any device connected to the network is the same type of device. Then the printer determines which of these same type devices have firmware older than firmware of the printer (S23). With respect to each device with older firmware (S23:YES), the firmware of the device is rewritten in S27 based on the firmware of the printer. As a result, the firmware of devices connected to the network can be easily rewritten. All other devices that are the same type as the printer can have their firmware updated into a firmware at least as new as the version stored in the printer. Accordingly, labor required to manage the network system can be greatly reduced.