  A microscopic Hamiltonian reflecting the correct symmetry of $f$-orbitals is
proposed to discuss superconductivity in heavy fermion systems. In the
orbitally degenerate region in which not only spin fluctuations but also
orbital fluctuations develop considerably, cancellation between spin and
orbital fluctuations destabilizes $d_{x^{2}-y^{2}}$-wave superconductivity.
Entering the non-degenerate region by increasing the crystalline electric
field, $d_{x^{2}-y^{2}}$-wave superconductivity mediated by antiferromagnetic
spin fluctuations emerges out of the suppression of orbital fluctuations. We
argue that the present scenario can be applied to recently discovered
superconductors CeTIn$_{5}$ (T=Ir, Rh, and Co).
