A method and apparatus is provided for efficiently supplying a liquid with ions or radicals generated by plasma and so on, or for effectively sterilizing microorganisms present in a liquid or on the surface thereof. The method includes generating plasma in a gas phase by a plasma generation device, producing ions or radicals in the gas phase by the plasma electrophoresing the ions or radicals toward the liquid by an electric field applied to the produced ions or radicals and diffusing the ions or radicals into the liquid. The liquid is adjusted to have a pH value of 4.8 or lower for effective sterilization.
