The configuration includes a laser range finder (110), a scan mechanism (120), a distance-data acquiring unit (130), a memory (160), a human-body determining unit (140), which detects an object with possibility to correspond to a human body from acquired distance information, calculates a height and a width of the object based on installation state information stored in the memory (160), determines that the object is a human body when detection of the object continues for a first predetermined time or longer in the case where a calculated object height is a predetermined height or more, and determines that the object is a human body when detection of the object continues for a second predetermined time longer than the first predetermined time or longer in the case where the calculated object height is less than the predetermined height, and an alert-output control unit (150).