A rule generation device according to an embodiment includes: a database in which, for each fault, fault factor information including a fault factor part and a fault factor, fault events that occur due to this fault, a rule ID associated with a rule including a condition part and a result part are registered in association with one another; an importance degree determination unit determining, when fault events of a new fault that is a newly occurred fault are registered with the database, degrees of importance of the fault events of the new fault based on at least one of values calculated through statistical processing or analytical processing for information other than the fault events or overall information about the fault events, which are registered with the database; and a rule generation unit generating a rule for the new fault based on the degrees of importance.