【正】 The differential cross sections of <sup>42</sup>Ca(p,α)<sup>39</sup>K with <sup>39</sup>K in (3/2)<sup>+</sup> and (1/2)<sup>+</sup> states at E<sub>p</sub>=20.0 MeV are measured and analyzed by using microscopic DWBA calculation.The realpotential is calculated via density dependent realistic nuclear force in a double-folding procedurewhereas the imaginary potential is expressed in terms of Fourier-Bessel functions.An improvedcalculation is obtained and analyzed to understand the absolute amplitude problem.