Neutron star models with hyperon-mixed core are studied by a realistic approach to use the YN and the YY interactions consistent with hypernuclear data. From the compatibility of the theoretical maximum mass with the observed neutron star mass 1.44 M⊙ of PSR1913+16, the necessity of some extra repulsion in hypernuclear systems, e.g., a repulsion from three-body force, is stressed. It is noted that the increase of baryon degrees of freedom to avoid the short-range repulsion effectively is an essential mechanism causing the Y-mixed phase. © Società Italiana di Fisica and Springer-Verlag 2002.