[en] A theoretical investigation of isoscalar electric-dipole excitation in self-conjugate nuclei by electron inelastic scattering is developed. The strongly excited isoscalar dipole states can be understood by means of a semi-classical model, where a relative motion of two interpenetrating isoscalar parts with isotropic shapes is assumed. Also it is pointed out that the Yennie approximation for a large-angle scattering is reasonably applicable to our case. Finally it is shown that the isospin mixing affects Coulomb from factors in the region of a small momentum transfer appreciably