A controlling device includes a controller that executes control to functionally activate of, at least, a part of transmission lanes in multiple transmission lanes connecting a plurality of subsystems which run based on a lock-step method and an embedder that executes an embedding operation to realize a multiplexing state using the part of transmission lanes controlled to functionally activate by the controller and the plurality of the subsystems, wherein, the controller determines whether or not the embedding operation succeeds, determines, when the embedding operation fails, whether or not an embedding operation using another part of transmission lanes, of the multiple transmission lanes, different from the part of transmission lanes used in the failure embedding operation, and executes, when the corporation processing succeeds, control to functionally activate the another part of transmission lanes.