To provide a network confidential information control system capable of easily accessing a site while securing security, without storing authentication information and personal information in a communication terminal device and a mobile electronic device.

This network confidential information control system is constituted of the communication terminal device operated by a user, the mobile electronic device attached detachably to the communication terminal device, and a support server unit for storing log-in information, and the mobile electronic device stores a biometric authentication software having a biometric authentication means for biometrically authenticating the user, and for logging the biometrically authenticated user in the support server, and a browser-linked software link-operated with a browser, for notifying a URL on a log-in screen to the support server when the log-in screen with an input column for log-in information is opened, for automatically writing the corresponding authentication information in the corresponding input column of the log-in information when transmitted from the support server, for detecting a transmission operation when the user writes the authentication information in the input column to execute the transmission operation to the site, and for transmitting the written authentication information to the support server to be stored.