We investigate breakup dynamics in 6 Li elastic scattering on heavy targets (T = 209 Bi or 208 Pb) near the Coulomb barrier energy. Since the subsystem of 6 Li has a bound state as deuteron (n + p = d ), a four-body channel (6 Li + T → n + p + α + T) and a three-body channel (6 Li + T → d + α + T) get entangled during scattering as a breakup channel. Both channels are precisely treated with the four-body version of the continuum-discretized coupled-channels method (four-body CDCC). Four-body CDCC well reproduces measured elastic cross sections with no adjustable parameter. We then estimate the channel coupling effects by dividing the breakup channel into fourand three-body channels. It is found that 6 Li breakup is mainly induced by a three-body channel.