An intermediary device includes circuitry to: transmit, to a server, device information on a device to be monitored acquired from the device via a network; monitor a state of another intermediary device, the another intermediary device being configured to acquire from another device to be monitored device information on the another device and transmit the acquired device information to the information processor; and take over monitoring of the another device, which the another intermediary device kept monitoring, based on setting information for monitoring the another device monitored by the another intermediary device, when the state of the another intermediary device indicates that the another intermediary device has an abnormality.