We can usually control magnetism by magntic field and dielectrical behavior by electric field. Now, we try to be able to "control magnetism by electric field" or "control dielectrical behavior by magntic field". This effect is known as "magnetoelectric effect". At low temprature, this effct has already realized with TbMnO3，however it is too small to use as application. In order to use device, we design materials to realize (1) performing at room temprature and (2) large response of magnetoelectric effect. Moreover, we study the origin of magnetoelectric effect and make a search of new mechanism.