The physical mechanism of the anomalous lateral displacement of the transmitted finite-sized light beam in a thin dielectric slab configuration is investigated from the view point of the interference between multiple light beams, due to the multiple reflections. The physical restriction, which agrees the mathematical condition of stationary phase approach, is advanced. Numerical stimulation shows that the anomalous lateral displacement is produced by the reshaping of the transmitted components undergoing different phase shifts due to the multiple reflections inside the slab. From the view point of a beam as a whole, the lateral displacement can be understood by the fact that the entire transmitted beam is the result of reshaping of the multiply transmitted beams.