E-book sales have exhibited explosive growth recently. A glimpse of this trend occurred as early as about 30 years ago, when E-books were used as media for circulating CD-ROMs and PCs. Their recent popularity is largely attributable to the popularization of mobile terminals such as smart phones. The authors classified the previous e-books into the first–third generations and later into 4G e-books, and analyzed the latter. The characteristics of 4G e-books are classifiable into the following three points: (a) instant search for book contents, (b) close relation between book contents and readers, and (c) reduction of expenditures for book contents. The TSP model, a novel e-book sales method proposed by the authors, (1) enables readers who start reading to read a whole book free of charge during a certain period of time, and then shifts to a time fee. (2) It can set up this period for each book, and can do so for each reader individually and unrestrictedly. Moreover, analysis of readers' logs permits a bookseller to record purchasing behavior and plot a sales strategy for each customer. This paper demonstrates that the TSP model can realize the 4G e-book business.