To realize a novel particulate detector which optically detects particulate such as smoke or the like with high detection precision and minimum detection error.

When a smoke detector detects smoke, photoelectric current in a receptor diode 25 is reduced and photoelectric current in a receptor diode 26 is fluctuated due to the effect of scattered light so that a fluctuation signal (b) is output from an AND circuit 45, and the output signal (e) from a comparator 48 becomes high in potential, then a MPU confirms the existence of the fluctuation signal (b) and the high potential of the output signal (e) to let a buzzer circuit 53 generate an alarm tone. In the case the smoke detector does not detect smoke, but its optical system is contaminated by smoke or the like and photoelectric current in the receptor diode 25 is reduced as the transmission rate is lowered, a transmission signal (d) becomes high in potential, but the fluctuation signal (b) is not output or is very small so that the AND circuit 45 does not output the fluctuation signal (b) and does not generate any alarm.