PURPOSE:To detect even a body to be examined which does not emit infrared rays, by arranging a pyroelectric infrared ray sensor in the focus position of a concave reflective mirror and connecting a band-pass filter and a signal processor and providing an infrared ray emitting body in front of the concave reflective mirror. CONSTITUTION:A pyroelectric infrared ray sensor 22 is provided in the focus position facing a reflective face 21 of a concave reflective mirror 20, and the output of the sensor 22 is outputted to a band-pass filter 24 and a signal processor 25 through a signal amplifier 23. An infrared ray emitting body 26 is set in front of the reflective mirror 20. If a body 27 to be examined such as a human body which emits infrared rays 28 appears in a detection area, the sensor 22 detects it and outputs a signal to the signal processor 25. If a body 27' to be examined does not emit infrared rays, infrared rays 29 having a prescribed frequency from the infrared ray emitting body 26 are reflected on the surface of the body 27' to be examined, and the reflected light is detected by the sensor. This output is inputted to the signal processor 25 through the band-pass filter 24.