To provide a light extinction type smoke sensor and a light extinction type smoke sensing system, not affected by the relation with a background color or a diffusion state of smoke, and not affected by a positional shift of a light emission means.

This light extinction type smoke sensor 1 sensing smoke on the basis of an extinction rate of detection light projected from a light emission unit 10 to a monitoring range has: an imaging unit 20 imaging the monitoring range; a search processing part 23b searching for a light emission face of the detection light by the light emission unit 10 or a reflection surface of the light emission face from an imaged image; a luminance calculation part 23c calculating a luminance of the searched light emission face; and a decision part 24 deciding presence/absence of generation of the smoke in the monitoring range by comparing the calculated luminance of the light emission face or a change amount of the luminance with a prescribed threshold value.

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