| CPC G01N 21/255 (2013.01) [G01N 21/3504 (2013.01); G01N 2201/0637 (2013.01)] | 12 Claims |

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1. A gas detection apparatus comprising:
a light emitting portion;
a light receiving portion;
a first mirror that has a reflective surface being a quadric surface and reflects light emitted from the light emitting portion; and
a second mirror that has a reflective surface being a quadric surface and reflects the light reflected by the first mirror to the first mirror, wherein
the quadric surface of the first mirror and the quadric surface of the second mirror have convex portions facing in a same direction,
the first mirror reflects the light reflected by the second mirror to the light receiving portion, and
when one surface of a substrate on which the light emitting portion and the light receiving portion are mounted is used as a reference plane, the first mirror and the second mirror are provided at positions higher than the reference plane and have different heights.
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