A plant-monitoring system includes: at least three detection elements, the detection elements being at least one type of detection element for monitoring a subject being monitored; a detection network configured by disposing the at least three detection elements in a plant; a storage unit that receives detection data from each of the detection elements to record the detection data as recorded data; and a processing computing unit. The processing computing unit receives the detection data from each of the detection elements, determines presence or absence of a fault by comparing the detection data with the recorded data, and in a case where occurrence of a fault is recognized, identifies a place of occurrence of the fault based on the detection data, and transmits the result of the place of occurrence of the fault to a predetermined incident response team.