To provide a reciprocation movement platform seat of a conductivity detector for enabling anyone to easily confirm installation positions in a state that a detection section of the conductivity detector is inserted into a tip of a meter main valve while a sample is measured, and in a state that the detection section of the conductivity detector is extracted to a position in which it is not clamped by the meter main valve while the sample is not measured independent of feeling based on an experience of a maintenance personnel.

The reciprocation movement platform seat comprises: a base for attaching the conductivity detector; a horizontal rod for fixing the base; and a box for inserting and extracting the horizontal rod, and limiting a movement range of the base. When the horizontal rod is inserted at the maximum, the box places the base in the installation position in a state that the detection section of the conductivity detector is inserted into the tip of the meter main valve while the sample is measured. When the horizontal rod is extracted at the maximum, the box places the base in the installation position in a state that the detection section of the conductivity detector is extracted to the position in which the detection section of the conductivity detector is not clamped by the meter main valve while the sample is not measured.