This paper empirically examines potentials of the Internet as a singular macro-level space of the public sphere, statistically analyzing the Citizenship Involvement Democracy survey. With the focus on "who" participate in the public sphere, "what" they do there, "why" they do so there, and "where" their main sphere is, this study investigates whether a virtual space on the Internet has potentials as the public sphere by contrasting between online political activities and offline political activities. Results from ordinal logistic regressions and analysis of variance indicate the Internet fails not merely in contributing to the substantial improvement of absolute equality but also in enhancing the level of political participation greatly. The reciprocal causality between online and offline political activities implies the Internet facilitates online political activities by the existing participants in the offline public sphere rather than encourages new participants. The demographic pattern of participation in political communication on the Internet is not much different from face-to-face political activities. Education and income level sharply divides the level of political participation in both online and offline sphere. The Internet has not narrowed the gap in offline political activities by education and income. While the online public sphere shows the generational gap in the participation level, the racial gap is significant in the offline sphere. Political efficacy for the Internet and political interests are commonly strong predictors for the level of activeness in both spheres, but age, race and civic attitude make a conspicuous distinction in the models estimating offline and online political activities. The finding is not necessarily skeptic because the Internet extends a physical scope of political activities by the existing active participants to a cyber space. The Internet is, despite its technological maturity, still a new architecture for the public sphere, and thus its potential is not fully accomplished.