  To study the superconducting gap structure of BiS$_2$-based layered compound
NdO$_{0.71}$F$_{0.29}$BiS$_{2}$ ($T$$_{\rm c}$ = 5 K), we measured the thermal
conductivity $\kappa$, which is a sensitive probe of the low-energy
quasiparticle spectrum. In the absence of a magnetic field, there is only a
very small residual linear term in the thermal conductivity $\kappa_{0}$/$T$ at
$T$ $\rightarrow$ 0, indicating the absence of a residual normal fluid,
expected for nodal superconductors. Moreover, the applied magnetic field hardly
affects the thermal conductivity in the wide range of the vortex state,
indicating the absence of Doppler shifted quasiparticles. These results provide
evidence that NdO$_{0.71}$F$_{0.29}$BiS$_{2}$ is fully gapped superconductor.
The obtained gap structure, along with the robustness of the superconductivity
against the impurity, suggest a conventional $s$-wave superconducting state in
NdO$_{0.71}$F$_{0.29}$BiS$_{2}$.
