PROBLEM TO BE SOLVED: To provide a surface treatment method for bringing out an excellent surface treatment effect by performing a coating treatment on the powder surface without using additive or dispersant, or by suppressing the used amount, and a powder on which a coating treatment is preformed by the method, and furthermore a cosmetic containing the surface-treated powder.SOLUTION: Such a method is accomplished by irradiating plasma to a powder in water, as pre-treatment of surface treatment of the powder. That is, the pre-treatment is performed by having the configuration of the electrodes to generate plasma to be such that the one of the pair electrodes be in a state submerged in water, or be in contact with water surface, and the other electrode be in a state placed in the air above water surface, and by applying a high voltage between both electrodes to generate plasma. Also, in this pre-treatment by plasma, the powder is in water and is in a state in which the powder surface is coated with water.
