The purpose of the present invention is to appropriately assess the respective states of a plurality of systems after a fault has occurred. If direct communication is suspended with any of a plurality of external systems which are installed one for one in each of a plurality of second facilities, a computer which is installed in a first facility assesses that a host system is in an isolated state. For a first external system, from among the plurality of external systems, for which a time greater than or equal to a prescribed time has elapsed from a last alive verification time, the computer assesses that said first external system is in a stopped state. For a second external system, from among the plurality of external systems, with which the direct communication is possible, the computer assesses that said second external system is in an alive state. If a third external system is present with which the time greater than or equal to the prescribed time has not elapsed from the last alive verification time and for which direct communication has been suspended, the computer assesses, on the basis of a prescribed condition, that either the host system or the third external system is to be placed in the stopped state, and that the other thereof is to be placed in the alive state.
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