The α-particle reduced widths γα2 for the ground state in Po210 and Po212 are calculated on the basis of the nuclear shell model. The calculations are made taking the boundary condition in an approximate way into consideration. The effects of the configuration mixing of the parent and daughter nucleus wave functions on γα2 are examined and it is found that they give quite large contributions to γα2. Some features of the distortion of the two nucleon wave functions arising from the configuration mixing are discussed graphically. It is shown that the wave function of relative motion with the mixing of the level which is lowered from the upper band by spin-orbit force would correspond to the bound electron-pair in the superconducting metals. Although there are some unavoidable uncertainties in the course of the calculations, it is concluded that the wave functions derived by conventional shell model calculations can explain the major part of the experiment values of γα2.