  We present the nucleon form factors and root-mean-square (RMS) radii measured
on a (10.8 fm$)^4$ lattice at the physical point. We compute the form factors
at small momentum transfer region in $q^2\le 0.102$ GeV$^2$ with the standard
plateau method choosing four source-sink separation times $t_{\rm sep}$ from
0.84 to 1.35 fm to examine the possible excited state contamination. We obtain
the electric and magnetic form factors and their RMS radii for not only the
isovector channel but also the proton and neutron ones without the disconnected
diagram. We also obtain the axial-vector coupling and the axial radius from the
axial-vector form factor. We find that these three form factors do not show
large $t_{\rm sep}$ dependence in our lattice setup. On the other hand, the
induced pseudoscalar and pseudoscalar form factors show the clear effects of
the excited state contamination, which affect the generalized
Goldberger-Treiman relation.
