In the authors' previous studies, the dependence of ultrasonic wave velocity on the microstructural properties of solid materials under plastic deformation was investigated both theoretically and experimentally. From the results obtained, it has been found that the changes of longitudinal wave velocity under simple and pure shear states are quite different, on the other hand transverse wave velocity changes under both shear states are almost same. These results suggest clearly that the propagating character of ultrasonic waves is dependent upon the interaction between the propagating mode of ultrasonic waves and micro-structural material changes induced by damages due to plastic deformation. In this paper, therefore, to identify the dependence of longitudinal wave velocity on the point defect, the longitudinal wave velocity propagating in a pure Aluminum single crystal under the pure shear plastic deformation is examined for several combinations of crystal orientations and shear slip directions which are determined by the difference of the amount of point defect calculated by the finite element polycrystal model (FEPM).