The development of electronic paper, which has the merits of both paper and electronic displays, is being eagerly pursued. This study aims to clarify the factors of readability which is naturally realized by paper; clarified factors will yield good guidelines for realizing readable electronic paper. Our expectation is that reading style is an important factor determining readability. We evaluate the reading performance of three medium handling styles (vertical, horizontal, hand-held) using current electronic books (LIBRIe, ΣBook) and paper documents. Test results show, for both types of electronic books, that the “hand-held” style is superior in terms of lower fatigue and better readability. It is suggested that the readability of electronic displays can be enhanced by making them compact and permitting the hand-held reading style.