There are provided a treatment tank generating a gas phase around a rotating center of a rotating flow of a liquid by rotating the introduced liquid, a first electrode whose at least a part is disposed in the treatment tank and in contact with a liquid in the treatment tank, a second electrode disposed so as to be in contact with the liquid in the treatment tank, and a power source applying a voltage between the first electrode and the second electrode to generate plasma in a gas phase, the plasma is generated in the gas phase to generate modification components, the generated modification components are dissolved and dispersed in the liquid, and a modification liquid is generated and retained in the storage tank. The modification liquid is sprayed or scattered from a nozzle into a treatment target space via a supply pump in the form of mist.