An I/O module according to one embodiment of the present invention includes a receiver electrically connectable to a field device and configured to receive first information autonomously transmitted from the field device, a storage storing the first information received by the receiver, and a comparator configured to compare the first information stored in the storage and second information newly received by the receiver and to rewrite the first information stored in the storage with the second information newly received by the receiver when the first information stored in the storage is different from the second information newly received by the receiver.