Model-independent constraint on the neutrino mass spectrum from the neutrinoless double beta decay

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.