PURPOSE: To provide a desensitizing device which prevents ground contamination from occurring on a printed matter, by forming a roller brought into contact with an image-receiving surface or a surface part of the roller from a rubber material comprising particulate or fibrous cellulose.

CONSTITUTION: Cellulose used for rollers 1W6 is particulate or fibrous, and is generally produced by dehydrating and drying a refined pulp, then grinding the dried pulp and sieving the ground pulp. The cellulose is hydrophilic, and permits a desensitizing liquid 8 to favorably adhere thereto but repells oil components. The cellulose is used in a rubber material in an amount of 2W5pts. wt. per 100pts.wt. of a raw rubber. The rubber material comprises the raw rubber as a main constituent, to which a vulcanizing agent, a coloring agent, an inorganic pigment or the like is added. A desensitizing treatment is carried out by the conventional process. Even where a planographic original plate 9 with oil components adhered thereto is used as in the case of making the plate by an ordinary paper copying machine, a uniform desensitizing treatment is performed, and ground contamination will not occur on the printed matter.