This dissertation aims to show the meaning of the 'Formula of Humanity as End In Itself',which is the third formula of the fundamental principles of Kant's ethics.The formula of Humanity as End In Itself is the third formula of Kant's categorical imperatives. It is as follows : "So act that you use Humanity, whether in your own person or that of another, always at the same time as an end, never merely as a means."Now the question is: what this formula means. Namely, what does it mean that you use a person as an end? Moreover, what does it mean further that you use a person 'always at the same time' as an end?If the idea and uniqueness of Kant's deontological-practical ethics can be well conceived, we must acknowledge the view of his moral philosophy that human being itself is not a relative end but an absolute-highest end, and is also a moral agent of practical reason as an 'thing-in-itself'.Since human beings should not be a means, but must be an end in itself, we should not treat a person and his act according to the mechanism of causation, but understand him and his act in the dignity of human beings. This means that a person is not only a means phenomenally but also an absolute end as a moral subject.But I don't think that Kant denied a person to be treated as a means in the real world. For example, when we go to a restaurant and want to order a dish, there is a waiter and we use him as a means in order to order and to be served. At this moment,he is a means of 'medium' to reach the common and same end which both of us have. In other words, it is an 'mediated' relationship through the common and same end. By this relationship, both of us as an absolute end itself take part in the absolute end autonomically in every action.