PHOTO-ELECTRIC TYPE SMOKE SENSOR

PURPOSE:To improve the detecting sensitivity of smoke by preventing a light from being incoming to a photo detecting element when the smoke does not exist in a darkroom and decreasing a background noise. CONSTITUTION:For the light projected from a light emitting element 21 to a darkroom 13a, an irradiation angle is limited by a shading piece 34e and concerning a photo detecting element 22, a photodetection angle is limited by shading walls 35d. Then, overlapping between an irradiating range by the light emitting element 21 on the inner peripheral surface of the darkroom 13a and a photo-detecting range by the photodetector 22 can be avoided. When the smoke does not exist in the darkroom 13a, the light is prevented from being incoming to the photodetector 22 and the background noise is decreased. Thus, the difference of photo-detecting light quantity of the photo-detecting element 22 can be obtained for a case that the smoke exists in the darkroom 13a and a case that the smoke does not exist. Thus, the detecting sensitivity can be improved to the smoke.