  We calculate the binding energies for multi-nucleon bound states with the
nuclear mass number less than or equal to 4 in 2+1 flavor QCD at the lattice
spacing of a = 0.09 fm employing a relatively heavy quark mass corresponding to
m_pi = 0.51 GeV. To distinguish a bound state from attractive scattering
states, we investigate the volume dependence of the energy shift between the
ground state and the state of free nucleons by changing the spatial extent of
the lattice from 2.9 fm to 5.8 fm. We conclude that ^4He, ^3He, deuteron and
dineutron are bound at m_pi = 0.51 GeV. We compare their binding energies with
those in our quenched studies and also with several previous investigations.
