PURPOSE:To eliminate or soften anisotropy of a directional distribution of reflected infrared rays and reduce exceedingly the intensity of infrared rays which come to other detecting element after being reflected, by making the form of reflecting surface of an infrared reflection member elliptical such as circular or oval and the like. CONSTITUTION:A detector 1a is equipped with a circular reflecting surface of an infrared reflecting member 8a. The directional distribution of reflected infrared rays has an axial symmetry and does not indicate anisotropy in conformity with a Fraunhofer's diffraction phenomenon. Further, even though a part of infrared rays which are reflected by the infrared reflecting member 8a belonging to a certain detecting element 2a, penetrates a layer of a metallic silicide 6, the feature of this reflection member serves the purpose of relieving the intensity of the above infrared rays which come to other detecting element 2a by receiving residual reflection at a plane which is treated with antireflection coating 4 of a P-type silicon substrate 5.
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