Microwave sensor capable of preventing false alarms due to a bush or tree or the like swaying in the wind

A microwave sensor that transmits a plurality of microwaves of different frequencies toward a detection area and is capable of detecting a distance to a detection target object based on reflected waves of the microwaves from the detection target object present in the detection area, said microwave sensor comprising:

• a movement distance measuring device configured to measure, as a movement distance of the detection target object, an amount of change per unit of time in a distance to the detected detection target object;
• an alarm signal output control device configured to perform control such that an alarm signal is outputted when the movement distance measured by said movement distance measuring device is a predetermined determination threshold value or more;
• and
• a determination threshold value varying device configured to vary 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.