In a U(3) x U(3) quark chiral model of the Nambu-Jona-Lasinio (NJL) type wi
th the 't Hooft interaction, the ground scalar isoscalar mesons and a scala
r glueball are described. The glueball (dilaton) is introduced into the eff
ective meson Lagrangian written in a chirally symmetric form on the base of
scale invariance. The singlet-octet mixing of scalar isoscalar mesons and
their mixing with the glueball are taken into account. Mass spectra of the
scalar mesons and glueball and their strong decays are described.