The purpose of this study is to provide an opportunity for better understanding and application of 2009 revised elementary school mathematics textbooks through focus group's investigations on the elementary mathematics teacher's guide books. First, We survey previous studies on the teacher's guide books to make the frame of investigation. Next, We compose focus group(8 teachers) for 3~4th grades, and analyze the teacher's guide books according to ready-made frame: compliance of curriculum, accuracy and fairness of contents, selection and organization of contents. As results of investigation, system of organization of the teacher's guide books is needed. Goal, contents, teaching methods, and evaluations have to be consistent in describing mathematical terms. And errors in mathematics and mathematics education are examined more carefully. The teacher's guide books afford teachers many materials and informations to teach mathematics through classroom lessons. So more study on the teacher's guide books and developmental study for the model guidebooks is needed along with the revised curriculum and new textbooks.