In 1998, the revised Commercial Act introduced the loyalty duty of the Director. Here are two points of view are facing each other, because one regards the loyalty duty as a specified duty of card and the other regards it as a totally different thing from the duty of care. Major opinion takes a position to support the homogeneous doctrine which was the major opinion and precedents before the revision of the Commercial Act in 1998. Deciding whether a director breaches the duties required, it should be reviewed whether the scopes of loyalty duty and duty of care are identically same. It is necessary to analyze the legislative purpose of providing the loyalty duty and the mechanism of deciding whether the breach occurs. This thesis studies the Loyalty Duty in company laws of the UK, USA, Germany, and Japan. There are two views of the loyalty duty in the UK. One regards the nature of the Loyalty Duty as a negative duty (proscriptive duty), and the other regards the duty as a positive duty (prescriptive duty). Both of views do not deny its origin, evaluation, and the effect of breach. It was practically necessary to distinguish the Loyalty duty from the duty of care in the United States. Because the nature and the legal consideration of the duties are different. In Germany, Aktiengesetz (Company Act) does not provide explicitly the loyalty duty of the director though academic opinions and precedents recognized it. Japan experiences conflicts between homogeneous doctrine and heterogenous doctrine on the relationship of loyalty duties and duty of care. Japanese major opinion and precedents follow the homogeneous doctrine, however, recently heterogeneous doctrine is emerging and a few low level court decisions which are different from the conventional precedents are coming out. Anglo-American judiciary looks that the origin of loyalty duty is different from that of care duty, and is building precedents on loyalty duty to overcome the limit of duty of care which is not sufficient to require the responsibility of directors. If the Anglo-American legal principles are the basis of our loyalty duty, it is reasonable to differentiate it from the duty of care. It is necessary to change the view of loyalty duty, if there are limitations on duty of care for requiring the responsibility of directors, and that is why the legislator provided explicitly the duty of loyalty.