Abstract: An impurity scavenging system which scavenges impurities of off-gases discharged from a clean room of a production line for semiconductors. The impurity scavenging system has a gas introduction line through which gas to be processed (hereinafter referred as GSP) is discharged, a scavenging unit which stores scavenging liquid, a condenser for condensing vaporized liquid from the scavenging unit, a first pump which pumps the GSP of a discharging line connected with the downstream side of the condenser, a liquid source, a cleaning liquid line which connects the discharging line to a drain and a first valve having ports, including a first port connected with the condenser, a second port connected with the first pump, and a third port connected with one end of the cleaning line another end of which is connected to the drain, thereby selectively enabling a connection from the condenser to the first pump and a connection from the condenser to the cleaning line.