When a mechanical load is given to a cracked material, an undulation appears in surface profile around the crack. The undulation is caused by stress-strain concentration at the crack tip and its release near the crack center. If the load is very small and within the elastic deformation range, the material recovers the original shape after unloading and no damage remains. Therefore, this surface undulation by a small mechanical load can be used for detection of crack on the material surface. In this study, non-destructive crack detection method by nanometric change in surface profile is proposed, and the experiment and related finite element analyses were carried out for notched high-density polyethylene (HDPE) plates. Nonuniform height change by a small mechanical load around the notch on the surface of HDPE plate was measured by a laser scanning microscope. The height change distribution agreed with the analytical result.