1. A method of measuring dynamic panel stiffness of an outer panel for automobile parts by pushing an indenter onto a surface of an outer panel to be measured in a selected pushing direction intersecting the surface under a selected load to deform the outer panel and measuring a deformation state of the outer panel comprising: transferring grids arranged in a regular lattice form to a surface of a measuring site of the outer panel to be measured; arranging fiducial markers indicating predetermined three-dimensional position information on a periphery of the measuring site of the outer panel; pushing the indenter onto the surface of the measuring site of the outer panel under the load and moving the indenter in a direction perpendicular to the pushing direction, during which the grids on the surface of the outer panel deformed by loading of the indenter are simultaneously and repeatedly shot from plural positions by plural cameras; and calculating three-dimensional position information of the grids corresponding to the fiducial markers based on the shot image data to measure a change in the deformation state of the outer panel associated with the movement of the indenter, which is output as panel deformation data.