  The mechanism of incommensurate (IC) spin-density-wave (SDW) order observed
in the Flude-Ferrell-Larkin-Ovchinnikov (FFLO) phase of CeCoIn$_5$ is discussed
on the basis of new mode-coupling scheme among IC-SDW order, two
superconducting orders of FFLO with B$_{1{\rm g}}$ ($d_{x^{2}-y^{2}}$) symmetry
and $\pi$-pairing of odd-parity. Unlike the mode-coupling schemes proposed by
Kenzelmann et al, Sciencexpress, 21 August (2008), that proposed in the present
Letter can offer a simple explanation for why the IC-SDW order is observed only
in FFLO phase and the IC wave vector is rather robust against the magnetic
field.
