A nuclidic mass formula composed of a gross term, an even-odd term and a shell term is presented as a revised version of the mass formula constructed by the present authors and published in 2000. The gross term has almost the same functional form as in the previous formula, but the parameter values in it are somewhat different. The even-odd term is treated more carefully, and a considerable improvement is realized. The shell term is exactly the same as the previous one; it was obtained using spherical single-particle potentials and by treating the deformed nucleus as a superposition of spherical nuclei. The new mass formula is applicable to nuclei with Z ≥ 2 and N ≥ 2. The root-mean-square deviation from experimental masses is 666.7 keV, which is less than that of the previous mass formula, 689.8 keV. §1. IntroductionNuclear masses are important quantities to determine the ground state properties and reactions. Since the formulation of the Weizsäcker-Bethe nuclear mass formula, 1), 2) many mass predictions have been made. At the present time, the main purpose of the study of mass formulas is to predict reliable masses of unknown nuclides, especially neutron-rich nuclides and the superheavy nuclides. Some recent mass formulas have been applied to calculations of fission barriers and r-process nucleosyntheses.One way to reproduce the known nuclear mass values is to use mass systematics. For example, the mass formulas presented by Comay et al. and Jänecke et al. 3) are based on Garvey-Kelson-like systematics, 4) which take into consideration particle-hole configurations and yield accurate predictions of known experimental masses, though it is rather difficult to apply these formulas to unknown nuclei far from known ones. In the last decade, some mass predictions designed for wide nuclidic regions have been presented. Among these, we specifically mention two sophisticated mass formulas that give not only nuclear masses but also nuclear shapes

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