PURPOSE: To obtain a photoelectric smoke detector against which a wide monitoring space can be set without increasing the number of light emitting and receiving means.

CONSTITUTION: A driving section 41 selectively sets the orientation of a case 6 equipped with a light emitting and receiving means 1 and 2 in a plurality of directions. Detecting light rays emitted from the light emitting means 1 in various direction are made incident to the light receiving means 2 after they are reflected by reflecting bodies 51 installed to different locations from the case 6. Therefore, it becomes unnecessary to install the light receiving means 2 at every light emitting direction of the means 1 and, even when the means 1 and 2 are provided by one pair only, the monitoring space of this photoelectric smoke detector can be expanded.