  Proton charge radius is calculated from the electromagnetic form factor of
proton parameterized by the dispersion relation.
  The calculated charge radius is a little larger than that obtained by the
Lamb shift of the $\mu$ mesic atom. As the result is sensitive to the
experimental data of proton electric form factor at small momentum transfer,
more accurate data are required to draw conclusion if the result of the nucleon
form factor is different or not from that obtained Pohl et al.
