  The In-doped topological crystalline insulator Sn_{1-x}In_xTe is a candidate
for a topological superconductor, where pseudo-spin-triplet state has been
proposed. To clarify the spin symmetry of Sn_{1-x}In_xTe, we perform
^{125}Te-nuclear magnetic resonance (NMR) measurements in polycrystalline
samples with 0< x <0.15. The penetration depth calculated from the NMR line
width is T-independent below half the superconducting transition temperature
(T_c) in polycrystalline Sn_{0.96}In_{0.04}Te, which indicates a fully-opened
superconducting gap. In this sample, the spin susceptibility measured by the
spin Knight shift (K_s) at an external magnetic field of H_0 = 0.0872 T
decreases below T_c, and K_s(T=0)/K_s(T=T_c) reaches to 0.36 \pm 0.10, which is
far below the limiting value 2/3 expected for a spin-triplet state for a cubic
crystal structure. Our result indicates that polycrystalline
Sn_{0.96}In_{0.04}Te is a spin-singlet superconductor.
