Abstract
On the basis of the theory developed by Yosida, Okiji and Yoshimori on the singlet ground state of a system of conduction electrons and a localized spin coupled with an antiferromagnetic exchange interaction, the magnetic-field dependence of the ground state is investigated in logarithmic accuracy by collecting the most divergent terms in the integration kernel. The correctness of a previous result for the susceptibility obtained by an iteration method is confirmed in the weak coupling limit, and it is further concluded that in this limit the bound state does not disappear at a finite value of magnetic field, but approaches the normal state asymptotically at high field.