A position identifying unit is configured to identify the location of a monitored person in the horizontal direction and maximum height of the monitored person in the vertical direction on the basis of top-down image data acquired by an upper image sensor provided above a monitored area capturing an image of the monitored area and lateral image data acquired by a lateral image sensor provided along a side of the monitored area capturing an image of the monitored area. An event determining unit assesses a fall-related event for the monitored person on the basis of a location in the horizontal direction, a maximum height in the vertical direction.