To provide a back-and-forth movement pedestal of a conductivity detector for allowing everyone to easily check the grounding position of the conductivity detector in the measurement of a sample where the detection section of the conductivity detector is inserted to the tip of an instrument master valve and the installation position of the conductivity detector in the non-measurement of a sample where the detection section of the conductivity detector is pulled to a position not inserted into the instrument master valve without depending on sensation based on the experience of a maintenance worker.

The back-and-forth movement pedestal comprises: a rail fixed on a foundation; a movable pedestal slidable along the longitudinal direction of the rail while the conductivity detector has been mounted; and a pair of stoppers fixed to the rail with a prescribed interval for regulating the slide movement of the movable pedestal in the rail. The stopper at the front side is installed according to the installation position of the conductivity detector in the measurement of a sample where the detection section of the conductivity detector is inserted into the tip of the instrument master valve. The stopper at the rear side is arranged according to the installation position of the conductivity detector in the non-measurement of a sample where the detection section of the conductivity detector is pulled to a position not inserted into the instrument master valve.