Objective: The aim of the study is to evaluate the difference of legibility between e-book and paper-book by using eye-tracker. Background: Despite of many researches on the e-book and paper-book, there are few researches on the difference between e-book and paper-book. In addition, the researches on the e-book were only dependent on the e-book reader. This study focused on the comparison of e-book and paper-book controlled with the same environments. Method: This study was conducted with $2{ imes}3$ within-subject design. Independent variables include the types of book (e-book, paper-book) and font sizes (8pt, 10pt, 12pt). Dependent variables are four measures of fixation duration, saccade length, blink rate and subjective discomfort. Analysis of Variance (ANOVA) with repeated measured design was used to investigate the main and interaction effects of independent variables on each of the dependent variables. The multiple comparisons were performed by post hoc analysis and Bonferroni correction was applied. Results: Fixation duration at e-book was longer than paper-book (p<0.01). Saccade length at e-book was shorter than paper-book (p<0.05). Blink rate at e-book was higher than paper-book (p<0.1). Subjective discomfort at e-book was higher than paper-book (p<0.1). Legibility at 8pt was better than 10pt, 12pt (p<0.01) in fixation duration, saccade length and subjective discomfort. Conclusion: It was found that the legibility at e-book are worse than paper-book from this study. These results indicated that the legibility of e-book was needed to be validated and improved to replace the paper-book. Application: This study suggests improving something related to fixation duration, saccade length, blink rate and subjective discomfort for betterment of e-book.