To warn immediately without lowering the alarm level that a subject fell from a bed and automatically determine whether the subject left the bed or the subject fell from the bed and record the result.

A floor sensor 1 to detect an object on a floor beside a bed is installed in order to detect a subject when he or she stands on the floor beside the bed, and a body sensor 2 which does not detect the subject when he or she falls from the bed is installed. Both when the subject leaves the bed to move and when the subject falls from bed, the floor sensor 1 warns when it detects the event. If the body sensor 2 detects an object after a certain period of time from that point, the body sensor 2 records that the subject left the bed to move as an event for warning and if the body sensor 2 detects no object after a certain period of time, it records that the subject falls from the bed as an event for warning.