To enable an adequate flow rate of sample water to be always distributed in an analysis line by providing a control valve in the analysis line in which sample water is continuously distributed, fully opening the valve with a start signal and automatically adjusting the valve at a predetermined opening degree after a specified time.

The downstream of an automatic pressure reducer 8 is controlled at a proper pressure by a constant head vessel 10, part of sample water is always made to flow out from that overflow drain tube 11, and pressure-adjusted sample water is diverged in each analysis line by a divergence tube 12. For example, in a conductivity measuring line, the diverged sample water is discharged by a drain 20A through a branch tube 12a, a flow meter 17A, a control valve 18A, and a conductivity gauge 19A. The flow meter 17A measures a line flow rate and adjusts it to a proper flow rate by an inlet valve, and a conductivity gauge 19A continuously measures conductivity of sample water. The control valve 18A is fully opened by a start signal, extrudes and discharges air bubbles in the line, and is adjusted at a predetermined opening degree after a specified time. Thus, a proper flow rate of sample water can be always supplied to the analysis line.