The α elastic scattering on “non-alpha cluster” nuclei 44,48Ca as well as their “alpha cluster” isotope 40Ca has been successfully described by a potential derived from a single-folding model, in which the most of the nucleons in a nucleus exist in α-like clusters and the rest, in an unclustered nucleonic configuration. The folding potential does not need any renormalization factor over broad ranges of incident energies. The number of nucleons existing in the α-like clusters in the three Ca-isotopes has been found to be same and deduced as 34.