Logging information is necessary in order to understand a computer’s behavior. However, there is a possibility that attackers will delete logs to hide the evidence of their attacking and cheating. Moreover, various problems might cause the loss of logging information. In homeland security, the plans for counter terrorism are based on data. The reliability of the data is depends on that of data collector. Because the reliability of the data collector is ensured by logs, the protection of it is important problem. To address these issues, we propose a system to prevent tampering and loss of logging information using a virtual machine monitor (VMM). In this system, logging information generated by the operating system (OS) and application program (AP) working on the target virtual machine (VM) is gathered by the VMM without any modification of the OS. The security of the logging information is ensured by its isolation from the VM. In addition, the isolation and multiple copying of logs can help in the detection of tampering.