  It has been known since the beginning of this century that isomonodromic
problems --- typically the Painlev\'e transcendents --- in a suitable
asymptotic region look like a kind of ``modulation'' of isospectral problem.
This connection between isomonodromic and isospectral problems is reconsidered
here in the light of recent studies related to the Seiberg-Witten solutions of
$N = 2$ supersymmetric gauge theories. A general machinary is illustrated in a
typical isomonodromic problem, namely the Schlesinger equation, which is
reformulated to include a small parameter $\epsilon$. In the small-$\epsilon$
limit, solutions of this isomonodromic problem are expected to behave as a
slowly modulated finite-gap solution of an isospectral problem. The modulation
is caused by slow deformations of the spectral curve of the finite-gap
solution. A modulation equation of this slow dynamics is derived by a heuristic
method. An inverse period map of Seiberg-Witten type turns out to give general
solutions of this modulation equation. This construction of general solution
also reveals the existence of deformations of Seiberg-Witten type on the same
moduli space of spectral curves. A prepotential is also constructed in the same
way as the prepotential of the Seiberg-Witten theory.
