In this paper, the new concept of the dynamic singular configuration of flexible manipulators using the inverse dynamics method, we need to consider this dynamic singular configuration of flexible manipulators. Without considering it, the control around the dynamic singular configuration may become unstable. As an example, we derive the dynamic singular configuration of a 2-DOF planar flexible manipulator modeled by a virtual passive joint model. The characteristics of the dynamic singular configuration and the dynamic manipulability of flexible manipulators are discussed, and its experimental verification was performed.