Abstract We report the first clear detection of the Zeeman splitting of a CCS emission line at 45 GHz toward the nearby pre-stellar dense filament, Taurus Molecular Cloud 1 (TMC-1). We observed HC$_3$N non-Zeeman lines simultaneously with the CCS line, and did not detect any significant splitting of the HC$_3$N lines. Thus, we conclude that our detection of CCS Zeeman splitting is robust. The derived line-of-sight magnetic field strength is about $117 ± 21 \, μ$G, which corresponds to a normalized mass-to-magnetic flux ratio of 2.2 if we adopt an inclination angle of 45$^∘$. Thus, we conclude that the TMC-1 filament is magnetically supercritical. Recent radiative transfer calculations of the CCS and HC$_3$N lines along the line of sight suggest that the filament is collapsing with a speed of $∼$0.6 km s$^{-1}$, which is comparable to three times the isothermal sound speed. This infall velocity appears to be consistent with the evolution of a gravitationally infalling core.