An NDIR gas sensor has high responsiveness and less noise and includes a radiating section arranged to radiate an infrared ray, a detecting section arranged to detect the infrared ray radiated by the radiating section, and a sample cell extending between the radiating section and the detecting section along a route of the infrared ray and covering the entire circumference of the route of the infrared ray. The sample cell includes a plurality of cell elements extending along the route of the infrared ray. Side portions of the cell elements adjacent to each other overlap at an interval from each other.
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