Abstract: A data loss prevention system holds: a first file, which is one of an unencrypted file and a file that is automatically decryptable by the processor; a second file, which is not automatically decryptable; and process information indicating an allowed process that is allowed to access a file held by the storage device. The data loss prevention system receives a file access request by the process, judges whether or not the process is the allowed process by referring to the process information, executes judgment processing for judging whether or not network communication by the process is to be prohibited, and prohibits the network communication by the process when it is judged in the judgment processing that the process is the allowed process and that a file to be accessed in the file access request is the first file.