The possible forms of the anisotropic interactions between d electrons in cubic ferro-magnets in the theory of the polar model of metals are studied. Their contributions to the magnetic anisotropic constant K1(T) are calculated based on Dyson's theory of spin wave interactions with the method of the statistical perturbation theory. The accuracy of the calculation is restricted to the first order of the coupling constants of anisotropic interactions, and the results are given up to the T4 terms. It is shown that K1(T) varies roughly as the tenth power of the spontaneous magnetization in the temperature range where the theory is reasonable.