Recently VoIP applications have been popular due to the wide deployment of the wired/wireless Internet. Commercial VoIP services typically employ SIP and RTP for signaling and media transport protocols. Therefore, the VoIP service is vulnerable to a lot of threats because it uses the Internet where security is not guaranteed. For example, anomaly traffic cases such as hindering call connections, maliciously canceling calls, and deteriorating quality of voices have already been known. In this paper, the authors propose an anomaly traffic detection method for VoIP applications based on the flow monitoring traffic measurement architecture, called IETF IPFIX.