PURPOSE: To provide an infrared detection apparatus which can obtain a narrow detection area without using a Fresnel lens and easily finely adjust the detection area, and is inexpensive and easy to manufacture.

CONSTITUTION: The apparatus consists of a pyroelectric infrared detector S, circuit parts 43 necessary for processing detection signals output from the detector S, and a storing case 41 storing the parts. A predetermined distance (d) is spaced between the detector S and an infrared entrance hole 41a of the storing case in accordance with a required detection area. The detection area can be varied by setting a moving mechanism which moves the detector S close to or away from the infrared entrance hole, or adjusting a size of the infrared entrance hole.