A microwave sensor is provided with a moving distance measuring means (41) which measures a change quantity of a distance to a detected detection target object per unit time as a moving distance; a warning signal output control means (42) which controls to output a warning signal (Dout1) when the measured moving distance is a prescribed judgment threshold value or more; and a judgment threshold value changing means (43) which changes the judgment threshold value to a larger value when a status wherein the moving distance is at the judgment threshold value or more continues for a first prescribed period or longer or when a status wherein the moving distance is less than the judgment threshold value and a difference between the judgment threshold value and the moving distance is within a prescribed value continues for a second prescribed period or longer.