  The Imaging X-ray Polarimetry Explorer (IXPE) detected X-ray polarization in
the nearest Seyfert 2 galaxy, the Circinus galaxy, for the first time. To
reproduce the IXPE results, we computed the degree of polarization based on two
types of radiative hydrodynamic simulations: a parsec-scale three-dimensional
model and a sub-parsec-scale axisymmetric model with a higher spatial
resolution. In a series of papers, we confirmed that these models naturally
explain the multi-wavelength observations of the Circinus galaxy from radio to
X-rays. We used a Monte Carlo Simulation for Astrophysics and Cosmology code to
compute the linear polarization of continuum emission. We found that the degree
of polarization based on the parsec-scale radiation-driven fountain model was
smaller than that observed with the IXPE. The degree of polarization based on
the sub-parsec-scale model depends on the hydrogen number density of the disk
($d$), and the degree of polarization obtained from our simulation is
consistent with that observed with the IXPE in the case of $\log
d/\mathrm{cm}^{-3} \geq 13$. We investigate where the photons are Compton
scattered and imply that the origin of the X-ray polarization in the Circinus
galaxy is the outflow inside $0.01 \ \mathrm{pc}$. In this case, the degree of
polarization may change over a timescale of approximately ten years.
