The effect of the tensor force on the spin-orbit splitting in He5 and N15 is examined by using the meson-theoretic potential and the phenomenological Serber potential which are consistent with the experimental data of two nucleon systems. About a half of the experimental values of the spin-orbit splitting in the mentioned nuclei are obtained by the accurate computation of the second order effect in perturbation theory, whereas several previous calculations of this effect have yielded the splitting of wrong sign or of too small magnitude. As is pointed out in the present computation, the deformation of the closed shell core induced by the tensor interaction between the nucleons in the core is restricted so as to satisfy the Pauli principle with the outside nucleon. This restriction is mainly responsible for the present result of splitting energy.