PURPOSE: To uniformly atomize and supply moistening water from a low speed to a high speed by adopting a flat spraying nozzle means spraying moistening water atomized in response to a change in air pressure at the time of printing so as to form a flat spraying pattern for an atomizing nozzle means.

CONSTITUTION: To prevent the irregularity of a pattern at a low speed, atomization air pressure is lowered close to an atomization limit, and an air flow throttling hole 6 of an optimum diameter is set to an atomized air channel 5. At this time, a pattern adjuster 8 for flat spraying is closed. Then, to determine the flat spraying pattern, the pattern adjuster 8 is opened to adjust to a desired flat spraying pattern. The adjusted and set pattern adjuster 8 need not to be adjusted any more even if a printing speed varies. Under such type of atomizer and method, atomization air pressure and flat spraying air pressure can be set at a low pressure when the printing speed is low and at a high pressure when the printing speed is high even if the printing speed changes to very an atomizing amount of water. Accordingly, the splashing angle of an atomized drop can be constant, and a flat spraying pattern formed by moistening water sprayed to a roller can be made nearly uniform.