PURPOSE: To provide a fire sensor which can proximately arrange a PIN photodiode for receiving infrared ray so as not to be affected by red light emitted from a red light emission diode for confirming operation.

CONSTITUTION: A sensor base 3a is provided with a housing part 3c at the side of a housing. The housing part 3c opens at its bottom face, fixes/houses red light emission diode LED for confirming operation inside a space surrounded by a partition plate 20 in its center and arranges light emission diode LED0 and the PIN photodiode P0 on both sides of the space. A visual light cut filter 21 covers the opening at the bottom part of the housing part 3c excepting a room housing the red light emission diode LED for confirming operation. The partition plate 20 and the visual light cut filter 21 prevent the PIN photodiode P0 from receiving the red light of the red light emission diode LED for confirming and being affected by it.