  We show that the double quantization of Seiberg-Witten spectral curve for
$\Gamma$-quiver gauge theory defines the generating current of
W$(\Gamma)$-algebra in the free field realization. We also show that the
partition function is given as a correlator of the corresponding
W$(\Gamma)$-algebra, which is equivalent to the AGT relation under the
gauge/quiver (spectral) duality.
