The purpose of this paper is to clarify the sociological significance of "Liebe als Passion" written by Niklas Luhmann. Luhmann, a sociologist, is known for having opened up a new type of systems theory. Though he wrote many enlightening books, reference is rarely made to "Liebe als Passion" in sociological research. On the one hand, as love research, this book was probably too complicated. On the other, it was peculiar as a practical example of systems theory. But Luhmann himself considered this book central to his work. Indeed, this book might be rather eccentric as love research. However Luhmann's study of love is highly suggestive when forecasting future society and the relations between individualized persons. There are many points in this work meriting study especially with regard to the nature of individualized consciousness.