  The N=2 supersymmetric gauge theory with gauge group SU(2) is considered. The
instanton field is calculated explicitly using the superfield formalism. The
instanton-induced effects are encoded in the effective vertex in the
Lagrangian. This vertex produces the large distance expansion of the low energy
effective Lagrangian in derivatives of fields. The leading term in this
expansion coincides with the one-instanton-induced term of the Seiberg-Witten
exact solution of the model. All orders of corrections in derivatives of fields
are also calculated.
