[en] A third measurement of the electron anti-neutrino mass by tritium β-decay at INS was carried out after making some improvements for enhancing the counting rate. Langmuir-Blodgett film β-ray sources with a 5-times larger area (60 x 200 m m²) than those used in previous measurements were prepared, and a new position sensitive β-detector with a 6-times larger sensitive area was developed. Using this modified equipment, about 150000 events, more than one order of magnitude higher numbers than in previous measurments, were accumulated in the last 100-eV region below the end-point energy. A new upper limit of 13 eV was obtained on the mass with a 95% confidence level, including statistical and systematic uncertainties. (author)