Abstract: In an ATM switching unit, action information indicative of a cell of a presently operable system is stored into such a cell received from a line which is used as the line for the presently operable system, among cells received from duplicated lines, and also standby information indicative of a cell of a spare operation system is stored into such a cell received from a line which is used as the line for the spare operation system in an individual unit. Thereafter, the cells are transferred to a common unit. In this common unit, the cell into which the standby information has been stored is discarded by an IVC unit. Subsequently, transfer destination address information of the cell into which the action information has been stored is specified, and this specified cell is transferred to an output path thereof.