In recent years, reading through electronic books (e-books) has been increasing, but it is said that the comprehension of the contents is inferior to that of paper books. We propose two visualising bookmark methods to support the retention of sequential memory, one of the causes of poor comprehension, by focusing on the difficulty of “looking back” at e-books. To verify the effectiveness of the proposed methods, a comparative experiment was conducted to measure the degree of sequential memory retention and the ease of looking back on different reading styles. The results showed no significant differences in post-reading test scores for sequential memory retention. Still, the correlation between subjects’ reading comprehension and the test scores measuring ease of looking back at pages of an e-book was closer to that for paper books than the correlation for conventional e-book readers. The post-experiment questionnaire also showed that many subjects felt that the proposed methods were comfortable to look back at, indicating that the methods were highly effective in easing looking back.