SMOKE SENSOR

PROBLEM TO BE SOLVED: To provide a compact smoke sensor with high sensitivity allowing miniaturization and thinning of a smoke sensing chamber without lowering sensing accuracy.SOLUTION: The smoke sensor includes: a first light-receiving element 13 which does not directly receive emission light from a light-emitting element 8; and second and third light-receiving elements 17 and 18 which directly receive the emission light from the light-emitting element 8. The second light-receiving element 17 has a light-receiving surface 17A directed to a side opposite to a ground side while the third light-receiving element 18 has a light-receiving surface 18A directed to the ground side. Dust is easier to accumulate on the light-receiving surface 17A than the light-receiving surface 18A. Even if incident light amount is reduced due to the accumulation of dust in the light-receiving surface 17A, dust hardly accumulates on the light-receiving surface 18A to hardly reduce incident light amount. Accordingly, fluctuation of light-receiving amount by smoke (signal component) and fluctuation of light-receiving amount by dust (noise component) can be discriminated by a second light-receiving signal showing incident light amount to the light-receiving surface 17A and a third light-receiving signal showing incident light amount to the light-receiving surface 18A.