Abstract

A monitoring target plane is photographed with infrared-rays by each infrared-ray camera. A converter converts format of image data from each infrared-ray camera from analog format into digital format. A control unit, when detecting an abnormal area consisting of pixels having a density value over a fixed value in the image data, calculates an azimuth and an angle of elevation toward the sun from an abnormal location on the monitoring target plane that corresponds to that abnormal area, and judges that a fire occurs if an azimuth toward the abnormal location from the infrared-ray camera photographing the image data including the abnormal area is not coincident with the calculated azimuth toward the sun, or if an angle of depression toward the abnormal location from this infrared-ray camera is not coincident with the calculated angle of elevation toward the sun.