An instrumentation system according to one embodiment of the present invention includes a plurality of field devices, in which each of the field devices is configured to perform at least one of measuring and operation of a target, a connection device including a plurality of slots, in which I/O modules are respectively attachable to the slots and the field devices are connectable to the I/O module, and a host control device configured to individually set the I/O modules attached to the slots to have a redundant configuration or a non-redundant configuration and to operate a first I/O module having the non-redundant configuration, among the I/O modules attached to the slots, in a pseudo redundant configuration.