In a redundant system where multiple network interfaces can be switched, an interface switching device includes: a transformer for transforming automatic switch information between a predetermined type used for a predetermined network interface and each of other types used for network interfaces other than the predetermined network interface; a switch controller for performing switch control for automatic switch information of the predetermined type; and a control interface for connecting a first network interface to the switch controller via the transformer when first automatic switch information received from the first network interface is not of the predetermined type.