To provide a cleaning mechanism for exhaust duct of substrate treating device by which rollers with orifices in an exhaust pipe can always be rotated stably.

In the cleaning mechanism for exhaust duct of substrate treating device, a pair of rollers 14a and 14b which have orifices and are rotationally driven by means of a motor 20 faced to the orifices is provided in the exhaust duct 11 communicating with the inside of a substrate treating device, and reaction products (m) adhering to the rollers 14a and 14b are scraped off by means of scraping means (h) installed to the orifices. This cleaning mechanism is provided with a rotational speed detecting means 22 which detects the rotational speed of either one or both of the motor 20 and rollers 14a and 14b, and drives a warning means when the detection output of the detecting means 22 becomes slower than a prescribed rotational speed.