PROBLEM TO BE SOLVED: To enable, when removing minerals from raw milk by electrodialysis, a stable long-term electrodialysis without membrane contamination.SOLUTION: Provided is a desalination method of milk for removing at least a portion of minerals in a raw milk by an electrodialysis treatment, wherein, as a cation exchange membrane, there is used one including a polyvinyl alcohol-based copolymer having an anionic group-containing anionic polymer segment and a vinyl alcohol polymer segment, and having a microphase separation structure having a domain size (X) in a range of 0 nm