Effects of the structure'' of the pion on the pionnucleon scattering are discussed. A formal expression of the interaction kernel far the nucleon- antinucleon propagator is given, from which the effective Hamiltonian'' for the emission and absorption of one pion and that for two pions is derived, respectively. Effects of two-pion vertex, which is characteristic of the structure of the pion, seem to be not necessarily negligible compared with the effects of one-pion vertex, according to a very rough estimate of the order of magnitude of the coupling constant'' appearing in the interaction kernel ior the nucleon-antinucleon propagator. At present two standpoints are recognized with respect to the theory of the pion, i.e., the compound theory of the pion and the conventional local pion field theory. However, some important properties of both theories, are discussed by using the above method, and the qualitative properties concerning the isospin dependence of the pion-nucleon scattering matrix elements are obtained. Quantitative evaluation of the possible effects is not made, since for that purpose it is necessary to attack the details of the structure of the pion. It is shown, in the appendix, that the crossing symmetry fur the pionnucleon scattering holds even if themore » pion is considered to be composed of an arbitrary number of fermion pairs and bosons, provided that the primary interaction Lagrangian satisfies the integrability condition to assure the existence of propagators. (auth)« less