  We investigate the quark masses and mixings by including vector-like
down-type quark singlets in universality of strength for Yukawa couplings
(USY). In contrast with the standard model with USY, the sufficient $ CP $
violation is obtained for the Cabibbo-Kobayashi-Maskawa matrix through the
mixing between the ordinary quarks and quark singlets. The top-bottom mass
hierarchy $ m_t \gg m_b $ also appears naturally in the USY scheme with the
down-type quark singlets.
