PURPOSE: To provide a stopped flow system for preventing a mixture liquid in a measuring cell from spreading to the upstream side of a mixing point.

CONSTITUTION: Nitrogen gas in a cylinder 18 can be fed to a point X for mixing both liquids in a measuring cell 12 through a gas supply pipe 20. A third solenoid valve 21 is disposed on the way of the gas supply pipe. The third solenoid valve 21 is opened/closed at a predetermined timing to eject a specified volume of nitrogen gas at the mixing point X. A kind of valve function is exhibited by storing nitrogen gas at the mixing point X thus checking counter flow of the mixture gas in the measuring cell 13 and preventing the unmixed sample liquid from flowing into the measuring cell.