In an intruder identifying method and device, an intruder identifying sensor device identifies an intruder as a detection target to be originally detected by determining whether a variation style for a predetermined time of intruder intrusion state information based on the reception signal of the electric wave receiving unit during a time period from the time when the intruder identifying sensor device detects an intruder till the time when the intruder identifying sensor device does not detect the intruder is a predetermined variation style.