We describe a system which reminds users of not only the content of web pages but also which web pages we viewed in a session, why the pages were viewed, and what knowledge we acquire from them. We developed a module for automatically collecting user logs. We focus on meaningful period, which metadata is added to by extracting the log data. We call this type of period a “semantic period”. One type of semantic period is an “intensive period” which includes a lot of activity related to keywords, and the other type of period is an “active period” when a web page is actively shown in a window. We also describe an interface for retrieving information acquired in a browsing experience using the semantic period. Finally, we show that our method lets the user recall important knowledge based on the web pages viewed in the past more efficiently.