When external magnetic field is applied to magnetic material used, a magnetization phenomenon is caused, and big magnetic flux density can be obtained. The big magnetic flux density plays an extremely important role in a motor, a generator, a transformer, and a reactor which are the applied apparatus of the magnetic material in electrical engineering. Therefore, a magnetization phenomenon to obtain the big magnetic flux density and an iron loss produced in magnetization process in AC supplied are important material indexes for magnetic material. Here, an outline about the magnetization process and the iron loss is mainly described on an electrical steel sheet.