To provide a liquid substance detection sensor easy to process and reduced in the irregularity of the response characteristics of light.

The liquid substance detection sensor 21 is equipped with a first light path 22 for transmitting the light emitted from a light source 25, a curved part (light scattering part) 23 for scattering the light transmitted through the first light path 22 to the outside and a second light path 24 for transmitting the light penetrated from the curved part 23. The first light path 22, the curved part 23 and the second light path 24 are constituted of a light transmitting material, the scattering quantity of light to the outside in the curved part 23 is larger than the scattering quantity of light to the outside in the first light path 22 or the scattering quantity of light to the outside in the second light path 24.

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