In this research, we have built a system that visualizes the web browsing activities of network users for the assistance of the network administrator. This system visualizes the Web browsing activities of an organization by making the processing object not an individual user but a user group. The network administrator can comprehend the Web browsing activities of the organization by referring to the map. This system extracts a keyword from HTML files that the users browsed. Afterwards this system develops concepts from the extracted keyword using a thesaurus. In addition, this system creates a browsing model. The features of the browsing model are emphasized by weighting. After that, the browsing model is visualized by Kohonen's Self-Organizing Maps. The network administrator is assisted in grasping user web browsing behavior by this feature map. As a result, we think that we can assist the monitoring operation by the network administrator.