As to the dynamic characteristics of grinding process, the dynamic grinding force under such a particular condition as "an ideally round workpiece is to be ground vibrationally" was only analyzed geometrically so far, but not yet verified experimentally. In the case when a forced- or self excitedvibration becomes troublesome actually, some waviness which was already generated on a workpiece periphery is further ground vibrationally, hence, the previous theory must be revised to some extent. In the present study, the model of dynamic grinding mechanism in the case when a waviness consisted of an arbitrary amplitude and pitch is ground vibrationally, is first introduced, then the relation between a generated dynamic grinding force with an amplitude and phase of waviness is analyzed quantitatively, and this analytical result is experimentally verified by the help of a newly designed measuring equipment of dynamic grinding process. The study suggests that a new point of view, which includes the present results, should be required to make the mechanism of a self-excited vibration in grinding clear, because some waviness exists on a workpiece periphery in advance of any vibrational problem.