Provided is a photoelectric smoke sensor capable of correcting a sensitivity according to a state of contamination. The photoelectric smoke sensor includes: a storage section (6) for storing a zero detection value VN and an initial zero detection value; a moving average value calculating section (51) for calculating a moving average value of detection AD values output from a detection portion (1, 2, 3); a zero detection value updating section (52) for calculating a new zero detection value VN when a sensitivity of the detection portion is decreased as compared with that in an initial state, and in addition, when a rate of change in the moving average value with respect to the zero detection value VN exceeds a predetermined value; a detection AD value correcting section (53) for correcting the detection value; and a smoke-density computing section (54) for converting the corrected detection value into smoke-density data.