On the automatic magnetic measurement of magnetic soft iron by ring specimen, a change arises in the shape of hysteresis curve according to the change of measurering speed. And a phenomenon is observed as that the more measurering speed causes the more coercive force. The study was performed on the base of magnetic measurement by means of changing in thickness of specimens and these conditions of heat treatment, on the purpose of making clear about the actual state and the origin of that phenomenon. It was cleared that the phenomenon was originated with the delay of magnetization. And this can be explained owing to a view point of the penetration depth of magnetizing, that is depending on the frequency converted from speed of magnetizing and the permeability of materials.
