In recent years, Augmented Reality (AR) has attracted considerable interest from both academia and industry. Virtual Reality enables users to interact only with virtual objects in a virtual environment, but AR enables users to interact with both virtual objects and real objects in the real world. This feature supports application of AR to various fields such as education, driving, entertainment, and navigation. Especially, by application of AR to support workers in nuclear power plants, it is expected that working time and human error can be decreased. However, many problems remain unsolved to apply AR to real fields. In this lecture note, fundamental knowledge of AR is presented first including the overview of elemental technologies to realize AR. Then various AR applications to nuclear fields are described. Finally, future prospects are given.