The purpose of this study is to inquire into theoretical approaches to the teacher\'s reflection for developing teachers\' professional development program focusing on their practical knowledge. Three approaches-the type, the procedure and the stages of reflection-are explored. Also, the relations among these approaches are analyzed. The types of reflection are classified by the element of time; It is \'reflection-in-action\' and \'reflection-on action\'(Schön, 1983). Schön emphasized that \'reflection-in-action\' had more important implication to develop teacher\'s practical knowledge than \'reflection-on-action\'. Accepting his argument, this article regards reflection-in-action as a more important conception to develop teacher\'s practical knowledge in real classroom situation in this article. And \'reflection-in-action\' can be actually activated in classroom according to the procedure of reflection(ALACT cycle, Korthagen, 2001). The contents of reflection(what is teacher thinking now?) can be understood by using the stages of reflection. The types and procedure and stages of reflection can be integrated on the basis of the Korthagen\'s core reflection theory. Based on the analysis of these three approaches to the teacher\'s reflection, the suggestions on contents, teaching methods and period of the teachers\' professional development program are made.