| 摘要 |
A movement distance measuring device that measures, as a movement distance, an amount of change per unit of time in a distance to a detected detection target object, an alarm signal output control device that performs control such that an alarm signal is outputted when the measured movement distance is a predetermined determination threshold value or more, and a determination threshold value varying device that varies the determination threshold value to a larger value when a state in which the movement distance is not less than the determination threshold value continues for not less than a first predetermined period and when a state in which the movement distance is less than the determination threshold value and a difference between the determination threshold value and the movement distance is not greater than a predetermined value continues for not less than a second predetermined period.
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