Abstract: A passive-type moving object detection system is disclosed. The system includes an infrared detector, infrared sensors mounted on the infrared detector, a detection field including two columns of detection regions for monitoring a human intruder and two rows of detection regions for detecting a non-human intruder. The columns have a height corresponding to a human height, and an optical system is located between the infrared detector and the detection field. The infrared sensors have infrared accepting areas that include first and second sections. The first section optically corresponds to the columns and the second section optically corresponds to the rows. Each sensor receives infrared radiation from a moving object passing through the detection regions. The detector includes an arithmetic circuit that subtracts the peak values of signals generated by the detector and a decision circuit to compare the result with a reference level.