Optical concentration measuring device and optical member

An optical member used in an optical concentration measuring device comprising:

• a substrate;
• a light emitter on a main surface of the substrate and configured to emit light;
• a light receiver on the main surface and configured to receive at least a portion of the light emitted by the light emitter;
• and a light guide that is at least a part of an inner surface of a housing provided so as to cover the main surface, the light guide being configured to guide at least a portion of the light emitted by the light emitter to the light receiver, the optical member comprising:
• the light guide;
• a ceiling reflective surface that is a flat surface facing the main surface and is at least a part of a ceiling portion of the housing;
• a secondary reflective surface that is a quadric surface configured to reflect at least a portion of the light emitted by the light emitter;
• and a wall portion that connects the secondary reflective surface and the ceiling reflective surface, wherein,
• when a direction perpendicular to the main surface toward the ceiling reflective surface is a height direction, a maximum height of the secondary reflective surface from the main surface is a, and a minimum height of the ceiling reflective surface from the secondary reflective surface of the wall portion is b, then 0.5≤(b/a)≤2 is satisfied.