The β-matrix formalism is applied to the interaction of the charged meson with the nucleon, Harish-Chandra's Γ-formalism is used for introducing the invariant coupling terms, and the scattering matrix S is constructed covariant by Umezawa-Takahashi's method in order to avoid the troublesome “surface terms”. This S-matrix contains a normal independent direct coupling of nucleons besides the usual meson exchange couplings. It is shown that this additional coupling is due to the direct coupling included implicitly in the Lagrangian, and that the possibility, stated by Klein, of cancelling it by the corresponding term appearing in the whole interaction Hamiltonian is lost. The neutral and the charge symmetrical meson are also discussed briefly.