PROBLEM TO BE SOLVED: To provide a technique of accurately measuring the concentration of ozone water in a storage tank by suppressing the decrease in concentration of the ozone water during travel from the storage tank to an ozone water densitometer.SOLUTION: An ozone water concentration measuring system 1 which measures ozone water concentration includes an ozone water densitometer 4 measuring the concentration of ozone water which flows in from a storage tank 8 storing the ozone water via a pipe 5. The ozone water in the storage tank 8 flows into the ozone water densitometer 4 via the pipe 5 by dead weight.