  We perform a QCD sum rule analysis for the light scalar meson $\sigma$
($f_0(600)$) with a tetraquark current related to the instanton picture for QCD
vacuum. We demonstrate that instanton current, including equal weights of
scalar and pseudoscalar diquark-antidiquarks, leads to a strong cancelation
between the contributions of high dimension operators in the operator product
expansion (OPE). Furthermore, in the case of this current direct instanton
contributions do not spoil the sum rules. Our calculation, obtained from the
OPE up to dimension 10 operators, gives the mass of $\sigma$--meson around
780MeV.
