  We present a concise formula to relate the effective mass term of the
neutrinoless double beta decay to a single neutrino mass, two Majorana
CP-violating phases and four observables of neutrino oscillations for a generic
neutrino mass spectrum. If the alleged evidence for the neutrinoless double
beta decay is taken into account, one may obtain a rough but model-independent
constraint on the absolute scale of neutrino masses -- it is most likely to be
in the range between 0.1 eV and 1 eV.
