Smoke detector

The present invention provides a smoke detector that can detect smoke more quickly than prior smoke detectors. This smoke detector 11 comprises a light-emitting unit 111, a light-receiving unit 113, a light-receiving unit 114, and a control unit 118. The light-receiving unit 113 receives scattered light that was emitted from the light-emitting unit 111 and scattered by a particle group contained in the air inside a region A. The light-receiving unit 114 receives reflected light that was emitted from the light-emitting unit 111 and reflected by particles that pass through a position B. The control unit 118 counts the pulse waves that appear at changes over time in light intensity signals outputted from the light-receiving unit 114, and thereby measures the number of particles that passed through position B within a period equating to the most recent prescribed length of time. The control unit 118 measures the presence of smoke in an external space on the basis of the number of particles measured in that way, a