In this article, I would like to discuss the concrete impacts of Case Method on prospective mathematics teacher training. The purpose of this paper is twofold: 1) to investigate effects of Case Method for prospective teacher's view of mathematics, and2) to investigate their motivation to become a mathematics teacher via Case Method. For this purpose, a questionnaire was conducted as a preliminary survey on 64 prospective teachers(undergraduate students). We examined how subject's belief about mathematics changes. This was accomplished statistically. The t-test revealed that there was a significant difference in the Pre/ Post test score. Furthermore, to follow up on their thinking, 4 examinees from that survey were selected for semi-structural interview survey that proceeded flexibly according to the subject's reactions.