Nodal-line semimetals (NLSMs) contain Dirac-Weyl-type band-crossing nodes extending into shapes of lines, loops, and chains in the reciprocal space, leading to band topology and transport responses. Robust NLSMs against spin-orbit coupling typically occur in three-dimensional and in-plane isotropic materials which have more symmetry operations to protect the line nodes of band crossing, while the possibilities in exfoliatable materials with in-plane anisotropy are rarely discussed. Here, we demonstrate a robust NLSM phase in an exfoliatable in-plane anisotropic nonmagnetic semimetal . Combining angle-resolved photoemission spectroscopy measurements and first-principles calculations, we reveal multiple Dirac-type nodal lines with fourfold degeneracy in . Our findings suggest rich physics in structurally anisotropic topological materials and call for further functional exploitation based on them.