PURPOSE: To enhance the capability for measurement of high concentration residual chlorine in a liquid.

CONSTITUTION: The high concentration residual chlorine measuring system comprises a pump 8 for feeding a sample water to be mixed with pure water, a circuit 8b for operating the mixing ratio between the flow rate of the sample water measured by a sample water flowmeter 8a and the flow rate of pure water measured by a pure water flowmeter 6a, a reagentless residual chlorine meter 9 for measuring the concentration of chlorine contained in the mixture of pure water and sample water, and a multiplier 10 for multiplying the concentration of chlorine measured through the chlorine meter 9 by a mixing ratio.