  Terao's factorization theorem shows that if an arrangement is free, then its
characteristic polynomial factors into the product of linear polynomials over
the integer ring. This is not a necessary condition, but there are not so many
non-free arrangements whose characteristic polynomial factors over the integer
ring. On the other hand, the localization of a free arrangement is free, and
its restriction is in many cases free, thus its characteristic polynomial
factors. In this paper, we consider how their integer, or real roots behave.
