Japanese teachers share several pedagogical terms for describing the teacher’s key roles during classroom instruction. In particular, the term “Hatsumon”, which means asking a question in Japanese, is used for describing teachers’ key questioning that provokes students’ thinking at a particular point in the lesson (Shimizu, 1999). The current study aims to characterize teacher’s questioning in mathematics lessons by analyzing them at the phase of introducing mathematical concepts and procedures in Japanese classroom taught by a “competent” teacher. This study draws on the data from an 8th grade mathematics classroom that is a subset of the data in the Learner’s Perspective Study. Through the analysis, two key roles of teacher’s questioning were identified and discussed. First, it gives a clue to the students who are faced with difficulty in solving the mathematical task. Second, teacher’s questioning focuses on the processes of students thinking while they solve a problem individually or in groups, and provided an opportunity for them to look back their own process. The analysis suggests that timing and contents of questioning are keys to understand the competence of an experienced teacher who has clear ideas on how students’ learning should be considered in mathematics classrooms.