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).