In this paper, I will try to answer the question how the aesthetic idea in Kant’s aesthetic theory accounts for the universal validity of the subjective judgment of taste, and what the nature of the aesthetic idea is that makes such account possible. This claim about universal validity of the subjective judgment of taste in Kant’s philosophy is regarded to be problematic because of the seeming contradiction between the subjectivity of a judgment and its universality. What can solve this contradiction, from my point of view, is the role of the aesthetic idea that it plays in the judgment of taste and the subjective principle that puts cognitive powers of mind in a harmonious free relationship. The main feature that makes the aesthetic idea the source of the universal validity is its universal communicability expressed in the universally pleasurable feeling of the judgment of taste.