  We calculate the kaon semileptonic form factors in lattice QCD with three
flavors of dynamical overlap quarks. Gauge ensembles are generated at pion
masses as low as 290 MeV and at a strange quark mass near its physical value.
We precisely calculate relevant meson correlators using the all-to-all quark
propagator. Twisted boundary conditions and the reweighting technique are
employed to vary the momentum transfer and the strange quark mass. We discuss
the chiral behavior of the form factors by comparing with chiral perturbation
theory and experiments.
