As a result of the computerization of school education, teachers are faced with the design of new instruction problems which are different from usual instruction in the various points. The purpose of this study is to develop a system which can support teachers in the instructional design process flexibly and dynamically for their various requests. Main characteristics of this system are: 1) making use of ontology as a base, 2) facilitating teachers' instructional design process flexibly and 3) providing teachers with multiple entries to be supported by the system from various needs. For realization of these functions, this paper proposes FIMA (Flexible Instructional design support Multi-Agent system), which complies with the FIPA specifications. In this paper, we describe a structure of FIMA with its design rationale and its effectiveness.