To materialize a simple pyroelectric infrared sensor for detecting a central area and its peripheral area.

Single elements 35a, 24a, 24b, and 35b are horizontally disposed/formed in order on a pyroelectric-body substrate 1. The single elements 24a and 24b form a first dual element 24 while the single elements 35a and 35b form a second dual element 35. Infrared rays generated in substantially contiguous areas C, D, E, and F different from each other are condensed by a Fresnel lens of a lens dome 60 and applied to the single elements 35a, 24a, 24b, and 35b. A signal detected by the second dual element 35 with the infrared rays applied thereto is outputted from an FET2 while a signal detected by the first dual element 24 is outputted from an FET1. By means thereof, a person 100 is detected in the areas D and E (the central area) corresponding to the first dual element 24 and in the areas C and F (the peripheral area) corresponding to the second dual element 35 with the areas D and E interposed therebetween.

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