Recently, we can easily have opportunities to see English subtitles. For instance, they are included in movies and news. English subtitles are composed of various words whose difficulties are low to high. When a viewer tries to understand English subtitles, those words that do not match viewer's English skill have the possibility of making the viewer difficult to understand. This study classifies viewer's English skill into levels based on the TOEIC score, and proposes a system that is more effective in understanding English subtitles by adding annotation to them according to viewer's level.