Phonon dynamics of type-I clathrates Ba₈Ga₁₆Ge₃₀ has been studied at room temperature by inelastic neutron scattering for energy less than 9 meV. Optical phonons associated with large vibrations of Ba atoms filled in large tetrakaidecahedral cages are observed around E = 4.5 meV. Analysis based on a Born-Von Kármán force model shows that the longitudinal force constants between the Ba atoms and the oversized cages has a relatively small value of 0.011 ∼ 0.014 mdyn/Â. The results indicate that the Ba atoms are very loosely bound to the surrounding oversized cages that consist of Ga and Ge atoms.