This paper presents a research on the effects of graphic calculator in high school mathematics classes to enhance students' understanding of concept of limit. Recently, as the use of technology in business, industry, and science increases, the use of computer in school mathematics also increases rapidly. But the microcomputer has not had the impact that many people predicted. Therefore, objectives of the study are to investigate the effects of graphic calculator in the limit unit and to improve teaching-learning methods from analysis of its results. The results of the study are as follows. First, students' achievement of learning in limit unit where graph calculators were used was lower than those of the class where traditional teaching method used. Therefore, the use of graph calculator in the limit unit may not be effective for improving students' learning of the subject in overall. But, when the research groups were divided into upper level, middle level, lower level students according to achievements levels, the upper groups show meaningful differences and the instrument showed less effect in the functions rather than series, and also the procedural knowledge rather than conceptual knowledge questions. Second, from the interest-attitude test results conducted after the limit unit using graphic calculator, there were not meaningful differences in achievements between the two groups. But, in the 'mathematics as a process', experimental group obtained higher scores on average between the two groups, and shows meaningful difference. Therefore it might be referred that the use of graph calculator in the classroom let students have positive attitudes in 'procedural mathematics'. And, when the research groups were divided into upper, middle and lower groups, the upper and the middle groups of experimental group shows higher scores in the 'mathematics as a process' and have positive attitudes. And lower group of experimental group shows lower scores in the 'mathematics and self-consciousness' and have negative attitudes. From the above results, it might be concluded that the use of graph calculator in the limit unit is not as effective as the traditional instruction in the students achievements, and does not make considerable changes in students' interest and attitude in the classroom. But the use of graphic calculator makes a classroom's atmosphere more active, and it might be more effective in the early stage of instruction to help understand the concepts.