A network synchronization system comprising plural information processing devices (2a, 2b), wherein: a first information processing device among the plural information processing devices comprises a synchronization-use common storage unit configured to copy and then store first individual setting information for each user registered as being authorized to use the first information processing device, so that the first individual setting information can be shared with another one of the plural information processing devices (2a, 2b) other than the first information processing device; and a second information processing device among the plural information processing devices (2a, 2b) comprises a setting information unit configured to store second individual setting information for each user registered as being authorized to use the second information processing device, and a synchronization control unit configured to compare the second individual setting information for each user stored in the setting information unit with the first individual setting information for the corresponding user stored in the synchronization-use common storage unit, and to update the second individual setting information to latest individual setting information for each user based on a result of the comparison, wherein the synchronization control unit is configured to acquire common update information that is common to the plural information professing devices (2a, 2b), wherein the common update information is stored in the synchronization-use common storage unit and comprises definition information of antivirus software or update information pertaining to a function of the plural information processing devices (2a, 2b). a first information processing device among the plural information processing devices comprises a synchronization-use common storage unit configured to copy and then store first individual setting information for each user registered as being authorized to use the first information processing device, so that the first individual setting information can be shared with another one of the plural information processing devices (2a, 2b) other than the first information processing device; and a second information processing device among the plural information processing devices (2a, 2b) comprises a setting information unit configured to store second individual setting information for each user registered as being authorized to use the second information processing device, and a synchronization control unit configured to compare the second individual setting information for each user stored in the setting information unit with the first individual setting information for the corresponding user stored in the synchronization-use common storage unit, and to update the second individual setting information to latest individual setting information for each user based on a result of the comparison, wherein the synchronization control unit is configured to acquire common update information that is common to the plural information professing devices (2a, 2b), wherein the common update information is stored in the synchronization-use common storage unit and comprises definition information of antivirus software or update information pertaining to a function of the plural information processing devices (2a, 2b).