  This talk presents a lattice study of spontaneous chiral symmetry breaking
performed by the JLQCD and TWQCD collaborations with dynamical overlap
fermions. Our lattice configurations are generated in a fixed topological
sector. Since finite volume effects, partly due to the fixed global topology,
are mainly induced by pion fields, the dependence on the lattice volume,
topological charge and quark masses can be analytically predicted using chiral
perturbation theory (ChPT). We find a good agreement of Dirac operator spectrum
calculated on the lattice with the ChPT prediction including its finite size
scalings, through which the chiral condensate is determined with good accuracy.
