In this paper, we investigated the influence of technology, which gave an impact on students through the process of teaching & learning for the proof of an additive law of sine function in the mathematics education for the gifted. We chose students who were taking a course in enrichment mathematics at Science Education Institute for the Gifted in Mokpo National University, and analyzed their processes of a mathematical inference or conjecture, an algebraic description and a proof by visualization using technology. We found the following facts. That is, the visualization using technology is helpful to the gifted students in understanding principles and concepts of mathematics by intuition. Also, it is helpful to ones verifying various cases and generalizing principles. But, using technology can be a factor that disturbs learning of students who are clumsy with operating technology.