Abstract: A particle detecting system for detecting the number and size of particles generated in a process chamber of a semiconductor manufacturing system. The particle detecting system includes a small detection chamber and a particle detector. The small detection chamber not only has an internal space thereof provided outside a wall portion forming the process vacuum chamber so as to communicate with the process vacuum chamber, but also laser beam transmitting windows and scattered light extracting windows. The particle detector is arranged in an atmospheric environment outside the detection chamber and including a laser diode for emitting a laser beam into the detection chamber through the laser beam transmitting windows and photosensors for detecting scattered light generated within the detection chamber through the scattered light extracting windows. The detection chamber has such a structure as to be detachably attached to the process chamber.