To provide a method which can facilitate a pure water rinse confirmation process work after an ultrapure water production supply device is washed with a chemical solution and can do the washing efficiently in a short time.

At least a part of the liquid contact part of the ultrapure water production supply device which treats primary pure water to produce ultrapure water and supplies it to a use place, after being washed with a hydrogen peroxide aqueous solution, is washed further with a basic aqueous solution.