There is provided a water exchange meter being capable of automatically and continuously measuring the water exchange at the surface water/sediment interface in which a saturated vertical hydraulic conductivity of the sediment from the hydraulic head difference between a chamber and a storage pipe at a measurement location is measured, and after the measurement of the saturated vertical hydraulic conductivity, while the measurement device used in the measurement of the vertical hydraulic conductivity is maintained, a vertical hydraulic gradient between upper and lower portions of a chamber is continuously measured in situ.