It is suggested :from experimental data and theoretical analyses that the charge distribution function of the proton will become negative in the inner region. The analysis of Stanford data on the electron-proton scattering is reexamined, and a lower bound for (,-2)1, JJ is given model-independently from some general assumptions. As examples, two trial proton models are considered which are consistent with the prescnt Stanford data and in which the values of (,-2)1, J) are rather smallcr than the usually accepted ones.