To improve the transport efficiency by decreasing the common conveyer idle running time when switching the system of a Y-shaped system conveyer.

A converging conveyer is used as a common conveyer E to conveyers A-F constituting a Y-shaped system, and conveyers of R11, R12 are controlled not to cause idle running and converging of the conveyer E. For example, at the time of switching from R11 to R12, in the case where the starting and material release time TKR 12 of R12 (except common conveyer E/F) is larger than the material release time THR11 of R11 (except common conveyer E/F), prior to the material release of the conveyers A, B of R11, the conveyers D, C4-C1 are started, and release of R11 is started in the lapse of wait time α(=TKR12-THR11-Te(load-out time)) from the start of R12 so that the material of the former system R11 of the common conveyer E becomes load-out immediately before the material of R12 enters the common conveyer E.