Multi-instanton calculus in N=2 supersymmetric QCD

Microscopic tests of the exact results are performed in N=2 SU(2) supersymmetric QCD. We construct the multi-instanton solution in N=2 supersymmetric QCD and calculate the two-instanton contribution ${\cal F}_2$ to the prepotential ${\cal F}$ explicitly. For $N_f=1,2$, instanton calculus agrees with the prediction of the exact results, however, for $N_f=3$, we find a discrepancy between them.Comment: 11 pages, LaTeX, The result for $N_f=4$ flavors is added, which does not agree with Seiberg-Witten's result, but does agree with the result of hep-th/960720