A neutron spin-echo instrument has been developed and tested at the ST-1 beam port of the High-flux Advanced Neutron Application Reactor (HANARO). The phase evolution of a neutron spin was directly observed with this neutron spin-echo instrument. Polarized thermal neutrons (λ = 1.2 ˚A, polarization ∼= 0.37) were produced by the (200) reflection plane of a Co0.92Fe0.08 ferromagnetic single crystal and were then transported to the experiment area of the ST-1 beam port. The efficiency of the developed spin flipper was estimated to be 0.98 ± 0.01, and the spin flipping ratio of the instrument was measured to be 1.26. The measured spin echo point was in agreement with the expected value. The spin-echo time of our instrument was estimated to be in the range of a few picoseconds