PURPOSE: To sense the existing position and activity direction of a human body using a low-cost and simple structure device by segmenting and guiding infrared radiations collected by a Fresnel lens into predetermined segments, and sensing infrared radiations after filtering.

CONSTITUTION: A composite Fresnel lens 101 collecting infrared radiations is fitted to a lens fixing frame, and the lower portion of the fixing frame is fitted to a stem 107. Plural leads pass through both sides of the stem 107, and the respective leads further pass through the drive board 106, on which plural infrared radiation sensors 108 and a reference element 112 are equipped, on the upper portion of the stem 107. Above the drive board 106 an infrared radiation filter 105 is fitted to the side wall of the stem 107. The infrared radiations radiated from a human body are focused onto the filter 105 by the Fresnel lens 101, and in this case, the incident infrared radiations are segmented by the partitions of the guide 102, for instance, into left, center, and right direction, and are incident on the infrared radiation sensor 108 through the segments.