  The Josephson current between an s-wave and a spin-triplet superconductor
Sr$_2$RuO$_4$ (SRO) is studied theoretically. In spin-singlet / spin-triplet
superconductor junctions, there is no Josephson current proportional to $\sin
\phi$ in the absence of the spin-flip scattering near junction interfaces,
where $\phi$ is a phase-difference across junctions. Thus a dominant term of
the Josephson current is proportional to $\sin 2\phi$ . The spin-orbit
scattering at the interfaces gives rise to the Josephson current proportional
to $\cos\phi$, which is a direct consequence of the chiral paring symmetry in
SRO.
