[Problem] To provide a membrane treatment method and a membrane treatment apparatus for ballast water using a membrane module, which are capable of inhibiting the formation of scale on the membrane surface to reduce fouling, using a simple installation.[Means for Solving the Problem] The membrane treatment method and the membrane treatment apparatus for ballast water using a membrane module according to the invention, having a membrane treatment tank 2 and a membrane module 1 provided in the tank for continuously performing filtration while ballast water is being passed thereto as raw water; wherein a positive electrode and a negative electrode are provided in the membrane treatment tank 2 so as to come into contact with raw water in the tank, and a current passing means is provided in the tank for applying a voltage between the electrodes.