To provide a leaving-bed detection system hardly causing troubles or degradation by measuring the deflection change of the frame of a bed accompanying presence of a person on the bed in a non-contact manner.

To a first frame to be deflected accompanying the presence of a person on a bed, a predetermined transmission wave is transmitted from a sensor part 11 disposed at a part considered as standstill with respect to the frame. When a reflected wave reflected by the frame is received by the same sensor part 11, a determination processing part 12 to which signals from the sensor part 11 are input determines presence/no presence of the leaving of a person from the bed by signal change corresponding to the change of an interval between the sensor part 11 and the reflection surface 82a of the frame, and notifies a leaving-bed state to a manager away from the bed. Thus, leaving from the bed is detected in a non-contact manner with the person, troubles and degradation hardly occur, erroneous contact and intentional contact by a person are evaded, the damage of the like due to a person are evaded, and leaving-bed detection performance is maintained over a long period of time.