PURPOSE: To inexpensively improve the releasability of paper to prevent the surface staining of the drier of a paper-making machine without lowering the thermal efficiency of the machine by mixing, atomizing and spraying a surface stain-preventing agent and air at the nozzle of the spray unit of a spray device.

CONSTITUTION: A surface stain-preventing agent and air are fed into a timing belt 14 having a liquid pipe 21 and an air pipe therein through the joint 13 of a driven belt-winding reel 12, mixed at the nozzle 19 of a spray unit 18 traveling in a spray device main body 27 disposed apart 10cm or more the surface of a drier, atomized by their extrusion pressure from a spray opening 29 at the center of a cap 20 and subsequently sprayed on the surface of the drier while the spray unit is moved, thereby preventing the staining of the surface of the drier of the paper machine, the surface stain-preventing agent being fed from a agent solution tank 3 equipped with a pump 2 having a flow controller 1, and the air being taken in through a valve 6, adjusted with a pressure-reducing valve 7 and subsequently fed from through a valve 8 and an air control member 10 equipped with a flow rate-control dial 9.