PROBLEM TO BE SOLVED: To provide concentration measuring method and apparatus of soluble manganese, capable of accurately measuring a soluble manganese concentration in water.SOLUTION: The concentration measuring method and the apparatus of soluble manganese according to the invention are used for measuring soluble manganese contained in a variety of water, such as industrial water, agricultural water, and purified water including tap water. The method and the apparatus can be applied to, for example, a water purification facility that causes raw water to pass through a filter to remove soluble manganese contained in the raw water. The method includes: supplying test water with an ozone gas to bring the ozone gas into contact with the test water (S3); and irradiating the test water with a measuring beam which is monochromatic light of a wavelength 400-500 nm, detecting an intensity of the measuring beam having passed through the test water, and acquiring a soluble manganese concentration in the test water bas
