  A possible mechanism for the horizontal line nodes in triplet superconductor,
Sr$_2$RuO$_4$, is proposed. We consider the interlayer Coulomb interaction, as
well as the on-site Coulomb repulsion, between electrons in different bands. In
the second order perturbation in the interband interaction, the effective
interaction becomes dependent on $\cos \frac{q_z}{2}$, resulting in the
horizontal line nodes.
