  Applying the unitary clothing transformation method in the model of charged
spinless nucleons and neutral mesons interacting via the three-linear
Yukawa-type coupling, the expression for the charge shift in the third order in
the coupling constant is derived. Being determined off the energy shell, the
ex-pression can be reduced on the energy shell to the explicitly covariant
form, providing the independence of the particle momenta. Comparison with the
cor-responding result of the Dyson covariant perturbation theory is performed
by es-tablishing the link between the old-fashioned perturbation theory and the
cloth-ing approach.
