A plant-monitoring system comprising: at least three detection elements (11, 12, 13, 14, 15, 16, 17), the detection elements (11, 12, 13, 14, 15, 16, 17) being at least one type of detection element for monitoring a subject being monitored and for transmitting fault detection data; a detection network comprising the at least three detection elements (11, 12, 13, 14, 15, 16, 17) for being disposed in a plant; a storage unit configured: to receive the detection data from each of the detection elements (11, 12, 13, 14, 15, 16, 17), and to record the detection data; and a processing computing unit configured: to receive the detection data from each of the detection elements (11, 12, 13, 14, 15, 16, 17); to obtain a normal range corresponding to the detection data from the storage unit; and to determine that a fault has not occurred in a case where all of the detection data are within the normal range, or to determine that a fault has occurred in a case where at least one detection data is outside the normal range; the system being characterized in that in the case it is determined that a fault has occurred, the processing computing unit is configured: to identify at least one position of the detection elements which transmitted detection data indicating that there is fault, as a place of occurrence of the fault; to identify a developing direction of the fault, based on a difference in detection data receiving times of at least two respective detection elements (11, 12, 13, 14, 15, 16, 17), wherein the processing computing unit is configured to set, as a start point, at least one detection element from which fault detection data was received first, and to set, as an end point, another of the detection elements from which the next detection data was received, and to identify, as the developing direction, a direction of region that expands from the start point toward the end point; and to transmit the result of the place of occurrence of the fault and the developing direction to a predetermined incident response team (40, 50). at least three detection elements (11, 12, 13, 14, 15, 16, 17), the detection elements (11, 12, 13, 14, 15, 16, 17) being at least one type of detection element for monitoring a subject being monitored and for transmitting fault detection data; a detection network comprising the at least three detection elements (11, 12, 13, 14, 15, 16, 17) for being disposed in a plant; a storage unit configured: to receive the detection data from each of the detection elements (11, 12, 13, 14, 15, 16, 17), and to record the detection data; and a processing computing unit configured: to receive the detection data from each of the detection elements (11, 12, 13, 14, 15, 16, 17); to obtain a normal range corresponding to the detection data from the storage unit; and to determine that a fault has not occurred in a case where all of the detection data are within the normal range, or to determine that a fault has occurred in a case where at least one detection data is outside the normal range; the system being characterized in that in the case it is determined that a fault has occurred, the processing computing unit is configured: to identify at least one position of the detection elements which transmitted detection data indicating that there is fault, as a place of occurrence of the fault; to identify a developing direction of the fault, based on a difference in detection data receiving times of at least two respective detection elements (11, 12, 13, 14, 15, 16, 17), wherein the processing computing unit is configured to set, as a start point, at least one detection element from which fault detection data was received first, and to set, as an end point, another of the detection elements from which the next detection data was received, and to identify, as the developing direction, a direction of region that expands from the start point toward the end point; and to transmit the result of the place of occurrence of the fault and the developing direction to a predetermined incident response team (40, 50).