A present-in-bed state monitoring system configured to monitor a present-in-bed state of a subject on a bed, the system comprising: a plurality of load detectors (11, 12, 13, 14) configured to be provided on the bed or under legs of the bed to detect a load of the subject; a center of gravity position calculating unit configured to calculate a center of gravity position of the subject based on the detected load of the subject; a waveform output unit configured to output a waveform including a respiratory waveform of the subject based on a temporal variation of the calculated center of gravity position; a center of gravity position determining unit configured to determine whether or not the center of gravity position is in an edge area of the bed; a body motion determining unit configured to determine whether or not the subject has a body motion based on the waveform including the respiratory waveform of the subject, the body motion being different from a respiration of the subject; a notifying unit configured to perform a notification about the present-in-bed state of the subject based on a determination result of the body motion determining unit and a determination result of the center of gravity position determining unit, and a notification control unit configured to cause the notifying unit to perform the notification based on the determination result of the body motion determining unit and the determination result of the center of gravity position determining unit, wherein the notification control unit causes the notifying unit to perform a first notification in a case that the center of gravity position determining unit determines that the center of gravity position is in the edge area of the bed and the body motion determining unit determines that the subject has the body motion, and causes the notifying unit to perform a second notification different from the first notification in a case that the center of gravity position determining unit determines that the center of gravity position is in the edge area of the bed and the body motion determining unit determines that the subject does not have the body motion. a plurality of load detectors (11, 12, 13, 14) configured to be provided on the bed or under legs of the bed to detect a load of the subject; a center of gravity position calculating unit configured to calculate a center of gravity position of the subject based on the detected load of the subject; a waveform output unit configured to output a waveform including a respiratory waveform of the subject based on a temporal variation of the calculated center of gravity position; a center of gravity position determining unit configured to determine whether or not the center of gravity position is in an edge area of the bed; a body motion determining unit configured to determine whether or not the subject has a body motion based on the waveform including the respiratory waveform of the subject, the body motion being different from a respiration of the subject; a notifying unit configured to perform a notification about the present-in-bed state of the subject based on a determination result of the body motion determining unit and a determination result of the center of gravity position determining unit, and