A redundant system includes a primary system including a first node and a second node, and a secondary system including a third node and a fourth node. When the secondary system in place of the primary system operates, the fourth node executes first takeover processing or second takeover processing, the first takeover processing taking over the primary system on the basis of data update information acquired from either a second inter-system transfer path or a second intra-system transfer path, and the second takeover processing taking over the primary system on the basis of both the data update information acquired from the second inter-system transfer path and the data update information acquired from the second intra-system transfer path.