Direct observation of the local layer response of an antiferroelectric liquid crystal to the step form electric field has been carried out by a time resolved synchrotron X-ray micro diffraction measurement. When an electric field was changed from high voltage to 0V, corresponding to the ferroelectric to anti ferroelectric phase transition, the local layer transformed from the bookshelf to the quasi-bookshelf structure within 0.3 ins. The horizontal chevron structure was found in both the phases, though the decrease in the horizontal chevron angle was observed during a period of 0.2 ins after turning off the electric field. In the antiferroelectric to ferroelectric phase transition process (from 0V to high voltage), the layer structure transformed to the bookshelf within 0.04 ins.