[en] We study transferred dressed spin effect (DSE) in ${}^3\text{He}$ atoms, and experimentally observe a triplet spectrum. It is induced by an ultra-low-frequency (ULF) oscillating magnetic field at 4 Hz in ground-state ${}^3\text{He}$ atoms. The ULF triplet is transferred to the metastable state through metastability-exchange collisions (MECs) and measured optically, which demonstrates 2 s coherence time of the magnetically dressed ground state. The result shows the possibility for the measurement of an ULF magnetic field’s strength and a scheme for optical frequency modulation.