Provided is a smoke sensor, in which labyrinth walls (12) are formed to have bent portions (12b) by bending the portions (12b) inside of a smoke sensing chamber (101) such that their leading ends (12c) are formed as smoke guide ends directed toward a smoke sensing zone (S). The labyrinth wall (12(#1)), as formed at a portion to confront a light receiving unit (11), is further constituted to have an ambient light shielding end (12d) diverged toward the outside of the smoke sensing chamber (101).
