The local chain motion of poly(vinyl acetate) (PVAc) in 20 wt% PVAc benzene solution was observed by broadband dielectric spectroscopy in the frequency range of 10 μHz–10 GHz at various temperatures between −20 and +40°C from the partially crystallized state, which is composed of a crystallized benzene phase and non-crystallized PVAc/benzene solution phase, below the melting temperature, T _m, of benzene to the liquid state above T _m. The relaxation time of the local chain motion of PVAc shows extremely strong temperature dependence below T _m. This chain motion of PVAc is the origin of the glass transition observed by differential scanning calorimetry for the partially crystallized state of the PVAc/benzene mixture below T _m.