This study analyzed the impact of extensive reading (ER) on the TOEIC score among Japanese high school students. ER was administered for three academic years to three grades each with 250 students respectively. The individual reading amount and their TOEIC scores were recorded by the English teacher. The students were encouraged to read 200,000 words per year mainly outside of the classroom. Students read 5,000 words per week, which is 10 minutes per day for students who read 100 wpm, for five days a week, during 35 weeks of school, plus 25,000 words during the long vacations. The study showed that these students scored 650 or higher on the TOEIC test. The study also explains how to implement ER in a regular Japanese high school without eroding the fixed curriculum, and how the involvement of the school library supported ER and student motivation.