  An anisotropic Kondo semiconductor CeOs$_2$Al$_{10}$ exhibits an unusual
antiferromagnetic order at rather high transition temperature $T_0$ of 28.5 K.
Two possible origins of the magnetic order have been proposed so far, one is
the Kondo coupling of the hybridization between the conduction ($c$) and the
$4f$ states and the other is the charge-density wave/charge ordering along the
orthorhombic $b$ axis. To clarify the origin of the magnetic order, we have
investigated the electronic structure of hole- and electron-doped
CeOs$_2$Al$_{10}$ [Ce(Os$_{1-y}$Re$_y$)$_2$Al$_{10}$ and
Ce(Os$_{1-x}$Ir$_x$)$_2$Al$_{10}$, respectively] by using optical conductivity
spectra along the $b$ axis. The intensity of the $c$-$f$ hybridization gap at
$\hbar\omega\sim50$ meV continuously decreases from $y=0.10$ to $x=0.12$ via
$x=y=0$. The intensity of the charge excitation observed at $\hbar\omega\sim20$
meV has the maximum at $x=y=0$ as similar with the doping dependence of $T_{\rm
0}$. The fact that the charge excitation is strongly related to the magnetic
order strengthens the possibility of the charge density wave/charge ordering as
the origin of the magnetic order.
