Congressmen are members of National Assembly and representatives of the public. Meantime, Congressmen carry out critical functions on national level, in order to successful represent democracy and parliamentary system. Also, according to representative democracy principles of free delegation and related prohibitions, Congressmen are politically responsible for the consequences of country’s decision or policy making, but not legally responsible for such consequences. However, the representative democracy system is changing, due to the changing trend of party oriented state and administrative state,transformation of electoral system, declining quality of Congressman, and more public involvement in political participation. Especially, the opinion of the public’s representative organization indicates the nation’s opinion and its democratic legitimacy is mandated to be checked through various ways, including electoral system, voting system, and exercise of human rights. For changed principle of representative democracy and parliamentarism to come true harmoniously, it is necessary to redefine and update the responsibilities of Congressmen. In this aspect, there has been active discussions recently, of measures to restrict commercial activities while Congressmen are in office. This should be highly praised since the discussion is the measure for itself, in order to recover Congressmen’s original functions and to ensure their reasonable parliamentary activities. According to current Constitution Law clause three, it defines “Congressmen can not hold concurrent office that is enacted by law”. This is because concurrent office holding is prone to hinder the spirit of balance of power, or is prone to influence paddling. Related regulations is set by National Assembly Act. According to article one of clause twenty-nine, of National Assembly Act, in spite of other regulations that prohibit certain political activities or concurrent office holding, Congressmen can engage in other posts except the office set by article one of clause one of National Assembly Act. The intent of the regulations that prohibit Congressmen holding concurrent office, is to ensure fairness and independence when they carry out their duties. However, there are loopholes in the current National Assembly Act, to allow concurrent office holding. This is against the spirit of the Constitution, due to the limited scope of the current regulations. As a result, this thesis demonstrates the necessity of reviewing of reasonable criteria and alternatives about the socially controversial issue of Congressmen with concurrent office holding. Accordingly, this research intends to come up with reasonable legislative alternatives after reviewing similar regulations about concurrent office holding in other major countries and Korea.