Neutron scattering shows that non-Fermi-liquid behavior of the heavy-Fermion compound CeNi₂Ge₂ is brought about by development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around antiferromagnetic wave vectors (1\2  1\2 0) and (0 0 3\4) at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector (0.23, 0.23, 1\2). The energy dependence of the spin fluctuations is a peculiar character of CeNi₂Ge₂ which differs from typical heavy-Fermion compounds, and suggests importance of low-energy structures of quasiparticle bands.

PACS numbers: 75.30.Mb, 71.10.Hf, 71.27.+a