The data related to our life experiences is called lifelog, which can easily be collected with mobile electronic devices in recent years. Although lifelog research has been conducted for a long time, practical applications such as a memory assistant system have not been fully developed yet. This is mainly due to the lack of methods to structurize the lifelog data efficiently. In our research, we developed a method for structuring a lifelog consisting of data from various sensors, focusing on event estimation with neural network. In an evaluation experiment, we captured lifelog data with a device that has various sensors, and then we estimated the events, i.e., the participantsf activities. As a result, the system correctly estimated events 70.4% of the time. We also created a lifelog viewer to visualized the data based on the result of event estimation.