  We show that the Garnier system in n-variables has affine Weyl group symmetry
of type $B^{(1)}_{n+3}$. We also formulate the $\tau$ functions for the Garnier
system (or the Schlesinger system of rank 2) on the root lattice $Q(C_{n+3})$
and show that they satisfy Toda equations, Hirota-Miwa equations and bilinear
differential equations.
