A thermal image acquisitor (3) is attached to a wall (4) or a ceiling (5) on a side of a head of a care recipient (1) in a case where the care recipient lies on a bed (2), and captures an image of the bed and its surroundings from diagonally above to acquire a thermal image. Reference setting circuitry (12) sets two reference lines (8,9) respectively corresponding to a left end and a right end of the bed in the thermal image, and a reference height (10) for determining sitting-up of the care recipient. Heat source detection circuitry (13) detects a mass (11) of a heat source in the thermal image. State determination circuitry (14) determines a state of the care recipient from a positional relationship between a safe area (15) enclosed with the reference lines and the reference height and the mass of the heat source.